Sam hears the whole thing.
He lays on his side with his face to the wall, back to Dean and Castiel in the next bed. Not that Sam needs to see anything. Dean makes sure he hears it all.
They've been fucking for at least an hour now. Sam had gripped his hands into the pillow the first time Castiel came, high keening prayer of Dean's name echoing through the room as the angel had come down Dean's throat, Sam gritting his teeth to fight his urge to put a hand on himself as he listened to the wet moans Dean had let out as he swallowed. He'd come later.
Castiel comes again while Dean's fucking him, Dean crying out with vivid praise for the tight heat gripping his cock as Cas shudders around him. Dean follows him closely, grunts and moans and sighs and all the filthy nonsense Dean always mutters as he pumps Cas full of it slipping and sliding under Sam's skin to make him tense for it, cock twitching at the thought of it.
Sam hears them go still, hears Dean whisper it, what Sam waits for every night, snick of the bedside light coming on.
“Go to him.”
Sam rolls over, ready as Castiel slides in next to him. Sam pulls the covers back and pulls Cas to his chest, smooth expanse of the angel's back damp with Dean's sweat, Dean's scent on him like a brand. Sam runs a hand down Cas' chest, fingers sticking against the tacky lines of angel come drying on it.
So Dean had left that for him. He's feeling generous tonight.
Sam swirls his index finger through the mess on Cas' chest, runs it in little circles as he nudges his nose up against that spot on the back of Cas' neck, little indent right above the knob of his spine where Dean's mouth had just been, breathes in the scent of Dean's lips and spit and sweat. Sam opens his mouth and runs his tongue over it, smiles at the little shiver Castiel gives, swipes across it a few more times before he moves down.
Sam's face settles in between Castiel's shoulder blades, hand on Cas' chest pushing him back into Sam so he can drink in the scent of Dean seeping into Castiel, closes his eyes and tastes Dean in his mouth as he inhales, salty earthy leather piecrust gunpowder musk of Dean, ozone ocean mist of Castiel underneath it. Sam just holds him there and breathes until he can't stand it any more, cock straining against Castiel's legs.
Sam sucks a wet mark onto either wing of bone before he rolls Cas over onto his back, his brother's sweat in his mouth sucked off their angel's skin, breath coming out in a rush as he looks at Castiel, lips shining and bruised from Dean's mouth. Sam wouldn't mind kissing him, but he won't.
There are things Sam can do, and there are things Sam can't do. Sam can't kiss Castiel, can't suck his cock or get him off, but there are lots of other things Sam can do with his mouth.
Sam comes up on his knees over Castiel, angel's pale chest rising and falling underneath him. Sam knows Dean can see as he bends down, mouth open to snake his tongue out, broad strokes of it as he licks all of Cas' come off his chest, works his way down to Cas' stomach, sucking and licking until the only thing left behind is a thin trail of Sam's spit all over him.
Sam gets as close as he dares to Cas' cock, hard again and curving up towards his belly, hot breath skating over it as Sam grips a hand behind Cas' knees and brings them up. Sam rests back on his ankles and looks below him, eyes slanting down as he pushes Cas' legs up, folds them in half and presses them to Cas' chest, everything falling open for Sam to see.
Sam licks at his lips as he takes in the sight of Cas below him, pale thighs spread wide, slick streams of Dean's come running down them, drying sticky on the cleft of his ass, Cas' hole puffy red and still open from Dean's cock, gape of it taking Sam's breath away as he watches the ring of muscle spread open under him twitch, white dribble of Dean running out of it.
Sam's cock pushes out a spurt of precome, clear drop of it leaking down on the bed as Sam stares, eyelids heavy, lets himself imagine.
Sam can't fuck Cas, but that doesn't mean he doesn't see it clear as day, see himself fist his cock to rest the head against Cas' hole, already stretched and fucked by his big brother's big cock, Dean's come leaking out as Cas pushes down to take Sam's cock all the way, tight stretch of him slicked up with Dean's spunk, leaking out of Cas with each thrust to soak Sam's balls sticky wet as they draw up so he can fill Cas right back up again.
Cas would love it, but that's not what Dean wants, not why he sent him over.
Instead, Sam pushes Cas' legs in harder to watch another trickle of Dean's come leak out, watches it trail down the crack of his ass before he leans down to settle himself between Cas' legs.
Sam knows Dean can't see it any more, but that's ok. Sam makes sure he hears it.
He starts slow, licks the trail of white running down the seam of Cas' ass, little swipes of his tongue running around the rim of Cas' hole, Cas moaning and leaking precome onto his stomach.
Sam presses his tongue flat against Cas' hole and holds it there, moves his neck in a figure eight that gets Cas bucking and tensing his legs under Sam's hands. Sam tries to make it last, lick and tease at Cas as long as he can stand, his own cock aching hard as he laps up every drop of Dean's come outside of Cas' hole, Sam moaning and smacking his lips loudly all for Dean.
Sam pulls his hands away from Cas' knees, knows Cas will keep them right there as Sam places a hand on either side of Cas' ass, digs his fingers in and pulls, stretches Cas as wide open as he can.
Sam presses his lips flush with Cas' hole and sucks, hollows his cheeks out as he closes his eyes and tastes Dean, salty bitter earthy hot gush of Dean over his tongue, moan of pleasure against Cas' rim loud enough to reach Dean's ears and make Cas rut his ass back against Sam's face.
Sam points his tongue and pushes it into Cas' hole, little flutter of Cas' muscle against him as he works it in, filthy wet sucking noises filling the air as Sam licks out every drop of Dean he can get to, swallows down everything his brother will let him have.
When there's nothing left in Cas, legs spread open wide, hard cock arching up onto his stomach, wet rim of his asshole flexing at Sam like an invitation, Sam rears back on his knees and wraps a hand around his cock.
He rubs his thumb into the shiny bead of precome at the slit, every dirty moaning grunting noise he has left in him coming out as he works himself, a few strokes and twists over the head of his cock all it takes to drive him over the edge, bites his lower lip hard and holds his cock angled down, watches as he paints Cas' ass white, ropes of his come shooting out to coat the angel spread out beneath him, even lands a few right into Cas' hole.
Sam leaves those there for Dean. He's feeling generous.
Sam leans down to lick up an errant white stripe running down Cas' thigh, holds it in his mouth as he leans up and over their angel, mouth already open, perfect empty vessel for Sam to fill up for his brother, wet slide of Sam's come into his mouth as Sam looks over at the bed next to his.
“Go back to him.”