Oh, G - fuck, fuck - Sam’s hand is at the back of his head, scratching lightly through his hair and pulling him down, his throat burning and tears pricking at his eyes as he swallows around Sam’s cock.
Vaguely, through the hazy curtain of Godyespleasejustlikethat caused by Dean fucking into him from behind, Cas realizes that Sam is petting him.
He whines softly, though it barely squeezes through his lips around Sam’s cock, his back arching involuntary as a big hand wanders from his neck down his spine, stroking him in long, soothing lines.
He can’t breathe - he can’t - there’s not - there’s too much heat racing through his body, too much pleasure sparking in his veins for him to do more than take, and he can feel something coiling tight tight tight in his stomach and his whole body’s tensing up and oh, oh, he’s coming onto the sheets beneath him, cock twitching untouched, spurting out sticky white stripes.
It’s Sam. His voice is quiet, and pitched low, and disappointed, and shame curls up in Cas’ tummy and tingles down his back like a tail between his legs.
Sam’s hand grips his hair tightly, pulling him up to look into hazel eyes. He can feel spit escaping down his chin, but he doesn’t dare try to catch it with his tongue, instead whining desperately in the back of his throat.
"I know," Sam says, carding his fingers gently through Cas’ hair. "I know you didn’t mean to."
Cas relaxes into the touch, nodding a little. No, he didn’t, he didn’t mean to come so soon.
Cas goes very, very still. Dean pulls out of him, and Cas closes his eyes and bites back a whimper.
And then the Winchesters must’ve communicated silently, because Dean’s tugging him down the bed, pulling him backwards with hands on his thighs until he’s about to fall off. Sam’s hand finds the back of his head again, pushing him down, guiding his nose to the come-slick sheets.
"Look at the mess you made, Cas." He pushes a little harder for emphasis, and Cas whines again.
"Clean it up." And that’s Dean, from somewhere beside him, surely watching as Cas slips out his tongue to lap at the dirty sheets.