Summary: In the physical literature about the n-body problem (n ≥ 3), sometimes reference is made to the impossibility of solving the n-body problem.
Warnings: Graphic m/m incest. Threesome. Pegging. Language.
Spoilers: Mild for "Soft Target", "Primacy" and "Black Swan"
Original Story: Just Three by emmademarais
AN: Many thanks to my betas. ♥
In the physical literature about the n-body problem (n ≥ 3), sometimes reference is made to the impossibility of solving the n-body problem.
The Three-Body Problem.
The first attempts to understand the 3-body problem were quantitative, aiming at finding explicit solutions. The three-body problem is much more complicated; its solution can be chaotic. The restricted three-body problem assumes that the mass of one of the bodies is negligible; the circular restricted three-body problem is the special case in which two of the bodies are in circular orbits (approximated by the Sun - Earth - Moon system).
Sliding—fucking—into Charlie is like...
No. Words fail. It's not like anything Don's ever done.
It's not like anything he's even ever thought about, though—watching Charlie's face, his mouth, as Don sinks inside him—he understands why not. Don understands with perfect and aching clarity why he never let this thought cross his mind before.
This is addiction.
"At Amita's place?" Megan waved the requisition reports he'd been waiting for in his face; Don switched his cell to his other ear and grabbed a pen. "Aw, Charlie, why don't we just have it at the house?" Don zigzagged his signature across the places Megan had marked with arrow tabs and handed them back. Typically, Megan didn't take the hint to leave, folding the reqs in her arms and standing over him.
"It's a special dinner." Charlie sounded distracted...which wasn't that unusual either. "Come on, Don. What's the big deal?"
"Says the man who doesn't have to go home afterward." Don raked his fingers through his hair. "That's like an extra hour on my commute each way, buddy."
Charlie sighed, the kicked puppy noise he'd been using—successfully, mind you—on Don since he was a kid. "Look, if you don't want to come, I'm sure Amita..."
"Whoa, whoa, whoa..." Charlie had been hanging out with their dad too much; that little guilt trip was classic Alan Eppes. "I didn't say that."
Megan rolled her eyes and stuck her tongue in her cheek. Don waved at her irritably.
"So you'll come?" Charlie didn't even bother to disguise the eagerness in his voice and Don wondered if he was too old to be wrapped around his little brother's finger this way.
Don slouched lower in his chair and stretched his knees out, sighing. "Yeah, Charlie. I'll be there."
"First dinner with the in-laws, huh?" Megan commented when Don flipped the phone shut and tossed it on his desk. "That's got to be nerve-wracking."
"What?" Don wrinkled his eyebrows at her. "No. Amita's had dinner with us lots of times. And she’s not exactly an in-law." He paused. Considered. "Yet."
"Mmm." Megan nodded, mouth pursed around her pen. "But it's her first time making dinner, right? " She smiled knowingly at Don's nod. "Much bigger deal."
Don shook his head. "Charlie didn't say..."
Megan laughed. "You're expecting Charlie to know the difference?"
"Good point. I'd better bring wine."
"I've had dinner with the Eppeses. Better bring lots."
Don feels Amita's manicured fingernail scratch a line between his shoulder blades, down the hollow of his spine. The touch softens when she reaches his ass, stroking between to circle his opening. Don's back flexes at her touch, his hips, driving him deeper into Charlie.
Charlie's groan, the way his fingers drive into Don's shoulders, the way his head thrashes on the pillow...it's completely uncontrolled.
Don’s never seen Charlie completely uncontrolled. He did this. He did.
Amita presses her finger into him and Don hisses, baring his teeth.
Don couldn't remember ever being to Amita's apartment before, though it felt like he should have at some point, if only when dealing with the Primacy game killings. Charlie was already there when Don showed up, shirts rumpled and untucked, belt missing so that his slacks hung low from the points of his hips, showing a little crescent moon of belly every time Charlie moved or reached for something. Between that, Charlie's swollen mouth, and the half-smile that wouldn't leave Charlie's face, Don had a pretty good idea of what was going on before he showed up.
Though he felt an internal Attaboy for Charlie, finally coming into his own, it made Don feel strange and restless in a way he couldn't explain. He paced around Amita's apartment and picking up and touching things at random, unable to be still.
Some of it was just foreign territory, he was sure. He didn't entirely like it, but he was becoming a creature of habit in a lot of ways that felt comfortable and safe. Amita's place didn't feel like either. And, since Charlie had the house, it probably never would.
But part of it, he thought, was also the glances Amita had given him from under her lashes as she'd straightened the rucked couch cushions. Ever since Val Eng, Don had carefully steered clear of any of Charlie's girls, or anyone Charlie might even think of as his girl, just to be safe. But he knew that look, frank and assessing, with just a hint of a smile. Watching Amita direct it at him, while she tidied the sofa that she and Charlie had almost definitely had sex on...
Charlie came out a moment later to announce dinner was ready.
"Did you know he used to dream about you?" Amita’s whisper is too soft to carry to Charlie, even as entangled as they are. "He told me." Her finger strokes deeper, too big to ignore, too small to give satisfaction beyond the low level buzz of penetration. "I watched him get hard, talking about it. Talking about you."
Don groans, his head falling forward on his neck. Amita’s teeth nip the nape sharply, racking him with shivers as the pain-pleasure rockets up and down his spine. "I sucked him off while he talked about you." Her finger slides out. Don opens his mouth but before he can summon sound—let alone words—she fucks into him again with two, really excellent stretch and burn that tears Don in half, stuck between the tightness of Charlie around his cock and Amita’s fingers inside him. "All those times you told him about your exploits…you never knew he wished those stories were about him. How he’d jerk off thinking about it." Amita grinds against the back of Don’s thigh, a wet-hot scritch of pubic hair, skin and the velvet that covers her harness.
Don cradles the side of Charlie’s face in his palm. Charlie’s eyes open, glazed, feverish, a look in them that Don’s never seen—or let himself see—before. "It’s true," Charlie admits, arching up, thighs clutching Don’s hips. "I...God… All of it. All of it is true." He reaches up and drags Don down to his mouth.
Don picked up his cell phone again. Text messages weren’t capable of mockery, but if they were, Don felt this one definitely would be.
Don sighed and tossed the phone across his desk again. The message had been sitting there for nearly three hours and Don still couldn’t figure out what to do about it. What to say.
Halfway through last week’s dinner, Amita had gotten up without a word and, unbuttoning her blouse, gone into the bedroom. Charlie had looked at Don, his expression unreadable, for a moment that seemed to go on much longer than it did. Then Charlie had gotten up and gone after her.
A week later, Don still doesn’t know why he didn’t leave. Why he sat there, spooning up increasingly smaller scoops of apple-cheddar tart while Amita and Charlie had increasingly loud sex just fifteen feet away. They’d left the door open but Don hadn’t looked, staring fixedly at his dessert until the plate’s pattern of flowers was printed on the back of his eyelids when he closed his eyes.
Don knew that he and Charlie hadn’t worked out all the old bullshit from childhood. Probably most of it would never get worked out; it would just become scars that ached in stormy weather. And this didn’t feel like revenge. Charlie was straightforward in his anger and Amita…Amita had more sense than that.
Don didn’t know what it felt like. It was a lot like when they played chess; Charlie had an endgame in mind and all Don could do was fumble blindly along until it revealed itself.
And then surrender.
Lips pursed, Don grabbed the phone, stabbed in an affirmative and hit send before he could change his mind.
"Wasn’t just girls, was it, Don?" Three fingers in him now and Amita sets the pace. She rocks into Don and he drives into Charlie, shuddering between them. "How long has it been since you had someone inside you? Since you trusted anyone enough to do this to you?"
Fire scalds through Don, shame and arousal. He’s never told anyone but Charlie about it, about him, and that had been under the deepest secrecy-between-brothers. Don doesn't remember exactly when he decided to go to the FBI, but he's known for a lot longer what a liability bisexuality would be.
"It's okay, Don." Amita's free hand cards through Don's sweat-damp hair. With the other, she finds and fondles his sweet spot, streaking lightning across his eyes, through his whole body. Don bucks hard and Charlie grunts, fingernails biting into Don's skin. Amita's mouth curve into a smile against Don's ear before she bites the lobe. "We're all family here, right?"
"I said 'Did you hear me, Don?'" Amita put her hands over his, stilling the circle of the dishtowel in his fingers around the rim of the plate.
Don didn't know how or what to answer, other than a simple affirmative. He nods. Yeah. He heard.
We want to have sex with you. Both of us.
We're not kidding, Don. This isn't a joke.
No, it's definitely no joke.
After last week's shenanigans, Don was man enough to admit he'd been thinking about Amita a lot differently than before. And she was a beautiful girl. Just because Don had mentally labeled her off-limits didn't mean he was oblivious to that. But Charlie...
Charlie was his brother.
"You don't have to decide now," Amita said and squeezed Don's wrists through the dishtowel. Don wasn't looking, but he felt her eyes on him, intense and sympathetic in a way that made Don feel embarrassed, like there was something wrong with him. "We know it's a lot to hit you with at once."
Yeah, no shit.
"Don." Charlie's voice did what Amita's could not, drawing Don's gaze from the plate in his hand to his brother's eyes, troubled and hopeful at the same time. His look twisted in Don's stomach and for a moment, Don thought he was going to puke. "It's not... You don't have..."
Don held up his hand. "I know, pal." It was amazing how calm he sounded. Don was amazed at how calm he sounded. "I just...let me think."
Don could tell how much this meant to Charlie by the speed with which he agreed, nodding almost frantically. "Yeah. Of course. I mean... Of course."
Don deposited the plate carefully in the wire drainer and slung the towel across the counter. He gave Amita a kiss on the cheek, Charlie a carefully measured clap on the shoulder, and then left the apartment, trading air-conditioned cool for the standing bathwater heat of a Los Angeles evening.
Then he threw up.
Don can't concentrate as Amita rubs the harnessed dildo along his cleft, the molded silicone head nudging across his stretched and opened hole. He puts his head down on Charlie's sweat-slicked chest, just breathing as Amita contracts her muscles and eases into him.
It's been almost two decades. Two decades since he's felt this, since he's let himself have this. Both Charlie's hands curve around Don's head. The hair is too short for Charlie to get a good grip, but he doesn't need to. Don feels glued to him, welded by more than sex and sweat.
As Amita stretches him over her fake cock, breath catching, Charlie draws Don's head up again, curling to reach his mouth. It's Charlie who controls the kiss, sucking at Don's mouth, licking and tasting, using his teeth, his tongue, the pressure of his lips while Don only pants and takes it, takes it all.
"It's okay," Amita whispers in another long, slow, sliding flex. Her arms curve under him, raking up his chest, curling around his shoulders to pull him back onto her. "We've got you, Don. You're okay."
He'd let himself forget. What this felt like. What it felt like to let himself need it. It feels strangely right to let himself have it again with Charlie, the person he trusts above all others. The one who will not betray him. The one he can't betray.
"Charlie looks beautiful, doesn't he, Don?" Amita buries herself to the root in Don, the waver in her voice and the trembling tense and flex of her hips—flush against Don's—showing she's not as cool as she presents herself. "God, both of you do. I knew you'd look like this, feel like this." She laughs, deep and joyful, pressing in and then starting the slow slide out. "You are the constant." She bites his shoulder, not hard enough to break the skin but hard enough that he'll feel it the next few days. "C'mon, Don. Look how bad he needs it, our boy."
Don looks. He can't stop looking, Charlie's face huge and too close, unfamiliar from this angle and the most familiar thing Don knows. Charlie's eyes are closed but Don's are open. All of him is open as they take him apart from both ends.
Amita laps at the bite, rough like a cat. "Let's finish it."
Third time pays for all; the next time, the invitation was his.
It would be an out and out lie to say that Don had a plan. He threw himself into the menu because those were the kind of details he could handle but anything—everything—beyond that, he'd purely be flying by the seat of his pants. It was a system that had worked for him before but his faith in his instincts was both better and worse than it had been.
Don wondered how he was ever going to explain this to his therapist.
Not that he was ever going to tell a shrink any such thing.
Charlie and Amita both hugged him when they came in the door and Amita kissed him, an open-mouthed smooch to the side of Don's mouth. Don let her pull away first, eyes darting to Charlie to gauge his reaction.
Charlie looked back at him. Just that. Just looked long and steady back at him until Don was the one who had to break eye contact, muttering about dinner.
Don had busted his ass cooking, but, sitting at the table with the two of them and the heavy weight of expectation, it might as well have been glue and paper for all Don could taste of it. Charlie kept looking at him between mouthfuls, not quite expectant, but not un-expectant, either. It was just Charlie, looking the way he always did and Don didn't know how to see him differently, how to see him as anything but Charlie.
He tried to picture Charlie's hand on his dick, tried to picture that wide, expressive mouth wrapped around his cock and though the thought didn't turn him sick like it did the day they'd asked him, it didn't get much of a reaction out of him either.
"You're not serious," Don said and whoops, there they went, no plan and only a shaky, impossible outcome.
We want to have sex with you. Both of us.
Charlie put his fork down with a clink and every appearance of calm which, frankly, Don just did not get. "We are serious. I'm serious."
Don's smile felt strange, pasted on and fragile. "But...c'mon. This wasn't your idea, right, Charlie?"
Amita reared back, but Don couldn't take her all that seriously considering the smile stretching her lips. "I think I should be offended at that," she said, sounding anything but. "But as it happens, no, it wasn't Charlie's idea, it was mine."
Charlie reached and took Amita's hand without ever taking his gaze from Don's face. "I want this too, Don. Don't count me out just because Amita thought of it first."
"So you want to fuck your brother." Just saying it like that, flat-out, made Don want to flinch but that was why he said it like that, so Charlie could hear it, in all it's ugly, naked glory.
Charlie opened his mouth, sucking in a breath, and then paused, picking out his words. "I want to share this experience with the two people I love most in the world."
"By fucking your brother."
Charlie smiled and dipped his head in Don's direction. "Yeah, Don. By fucking my brother. Is that okay?"
Don passed a hand over his face. "God, Charlie, I don't know." It took an enormous effort for him to get up and cross to the other side of the table. He put his hand over Charlie and Amita's joined ones, drawing their fingers apart. "And it doesn't bother you, the thought of me touching your girl...your fiancée?" Don lifted Amita's hand, pressed his lips into her palm. She tipped her head back to smile up at him, but Don's eyes were only for Charlie, watching his every reaction. "Like this?"
Charlie shook his head. "No."
Don let Amita's hand go and trailed his fingers up her arm. Her skin was warm, smooth and soft; the frail scent of her perfume gained a little in strength, spicier than most women Don was used to. Don let his knuckles brush the full surge of her breast, hearing the sharp intake of her breath, enjoying the way she shifted restlessly in her chair. After what the two of them had put him through in the past couple weeks, he felt entitled. When Don's fingers reached Amita's neck, he twitched aside the long coil of curls and bent to ravage her neck.
Amita arched into it, tilting her head to give him better access. Her hand came up and threaded across Don's head, tickling his scalp. Don tasted her skin, its sweetness, its resilience. He let himself lose himself in it the way he'd been wanting to for the past two weeks. Then he looked up at Charlie, waiting.
"I trust you, Don." Charlie looked as if he'd been drugged, pupils huge and blown wide, the fast, shallow race of his breath. Don didn't expect the hard, sudden jerk of his cock in his jeans at the sight, at the words, blood making him harden so fast he felt lightheaded. It was Charlie's turn to take Don's hand. The seconds it took Charlie to suck Don's fingers into his mouth seemed like eons.
At the first strong suckle of Charlie's lips, Don wondered if Charlie had a theory to explain that, the time displacement. Don bet Charlie did. The thought made Don laugh, strangled and shaking. Amita's arms crept around his waist as she ducked under Don's free arm and pressed her face into his side. His tongue tracing the line between Don's two fingers, Charlie canted an eyebrow in question.
"Okay," Don agreed, tilting his fingers down to distort the line of Charlie's mouth. Charlie still looked the same. Don finally realized that was pretty much the point. "Okay, let's...let's give it a try."
It doesn't surprise him when, afterward, Amita shows up at his place.
Don offers her coffee; she asks for tea and then sits with the mug held between her hands, not drinking.
"Hell of a weekend, huh?" It's such monumental understatement, but Don doesn't know what else to say about it. About them. He's trying not to think about it, which, of course, means he hasn't thought about much of anything else.
Amita smiles. "I like puzzles," she says finally.
"I like puzzles. Especially jigsaw puzzles. Always have." Her fingernails tap against the ceramic of the mug in sharp, brittle music. "Life with Charlie...it's like an endless box of puzzles."
"Well, that's great," Don says lamely, completely unsure of where she's going with this. "Right?"
"You were the part of the puzzle I couldn't get. No matter how far back into him I go...you're always there."
"I'm the constant," Don says slowly, a piece of his personal puzzle falling into place.
"Yeah." Amita gestures vaguely. She looks up at him, her message plain in her expression, if not her words.
Don's anger slams up from his gut, searing through his veins. "You brought me into this, Amita. I was... I was doing just fine on my own!" Don's not a hundred percent sure that's true, but it's at least ninety percent true and that's close enough for government work.
"I know that!" Amita shouts in return, the uneven dither of her mouth making the words flat and almost toneless. She fiddles a hand through her hair and, calmer, she says, "I know that, Don. I'm sorry. I thought..." Her other hand lifts from the table then falls flat again. She looks away. "I don't know what I thought. I think... I think Charlie needed it." Her gaze cuts back to his with a nearly palpable plea for him to understand.
Oh, Don understands. He understands all too well.
And what about me, Amita? Did you ever once think about what I need?
But Don understands that too. It's no mistake that Charlie is the sun in their erratic orbit around each other.
"And I needed it," Amita admits. "I needed to give him that. And I needed...I needed to understand."
Don's jaw aches with the sourness at the back of his throat. He can't answer her. He doesn't even know what he'd say.
"Charlie..." Amita's breath catches unevenly. "Charlie wants to postpone the wedding."
She gets up in a rush, her thighs jolting the table. Don imagines the bruises that will form, imagines the heat and swell of the contusions against his lips and feels blood tumble into his cock. Amita lurches away, her heels thundering sharply on the wood and Don watches her go.
At the door, Amita pauses, gaze flickering uneasily over him. Don looks back, not sure what he expects. "Dinner's at eight," she says finally, and though her eyes are wet, the corners of her mouth flick up into a smile. "Don't shower beforehand. We like you dirty."
The Two-Body Problem.
If the common center of mass of the two bodies is considered to be at rest, each body travels along a conic section which has a focus at the centre of mass of the system (in the case of a hyperbola: the branch at the side of that focus). The two conics will be in the same plane. The type of conic (circle, ellipse, parabola or hyperbola) is determined by finding the sum of the combined kinetic energy of two bodies and the potential energy when the bodies are far apart. (This potential energy is always a negative value; energy of rotation of the bodies about their axes is not counted here).