Derek forgets why he's there, when he slips in to find Stiles shoving his long fingers into himself, panting and frustrated and greedy even with three of them buried deep. Forgets his reasons for barging in to Stiles' room, and every question stumbling through his mind, and his name.
Stiles is so caught up he doesn’t notice, just rocks back to his thick knuckles, skin flushed red all over, cheeks blazing, his forehead pressed to the wall 'cause he’s so busy fucking himself—holding himself open for his own fingers to slide in slick and rough—that he can't balance on his knees. His eyelashes are damp. He pants, sobs, makes noise like he’s in an empty house, like he’s never had to worry the neighbors will hear, high-pitched, and pleading, and so, so strained.
Every cry is choked, dry, like he’s been at this for hours. Like the red of his hole around his knuckles isn’t enough of a clue. It’s like he can’t get enough.
Like he can’t get it right.
Derek’s exactly self-aware enough to know he's never been strong enough to walk away when he should, but he’s not sure who’s more surprised when his knees hit Stiles’ mattress, when he stalks across the ruined sheets like the predator he is.
Stiles just gulps dryly, throat sticking, mortification crawling with a darker flush across his skin, and Derek—
Derek just wants a taste.
"You’re so close," Derek says, chasing that blush with his nose. His teeth. "Want it so much, don't you." It’s nothing like a question. “Just look at you," he says, breathless like a run can never make him.
Stiles stutters his name, curls forward, pushes into the sudden cup of Derek’s palm. He doesn’t pull away.
"You're almost there." If he could, Derek would laugh, if he had enough breath he’d howl. Instead he twists Stiles’ wrist, pushes his thumb under the wet head of Stiles’ dick, and says, “Like this.”
There’s one more shove of Stiles’ long fingers, maybe two, Derek taps his thumb, whispers, “come like this and I’ll fuck you through the next one, stretch you like you’ve never imagined you could, fill you up so full you'll forget you've ever been empty. Fuck you 'til you can't remember not wanting me in you."
Stiles comes a whole three thrusts later, mewling, with Derek’s blunt teeth on the long curve of his neck, and Derek hopes he knows that Derek’s not letting go.