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He can hear them. Erica's breathy cries for more, Derek's low pitched grunts, the creaks of the floor boards from where they rut on the floor in the next room. He can hear them and he hates it.
Stiles doesn't have to be there. Derek has in fact told him many times to leave when this happens. Heat. Stiles hates that word, too, it makes people seem like animals, uncontrollable, out of control, nothing but biological need and damn whatever the living breathing person underneath wants. Sitting on the floor of the bedroom he usually shares with Derek, listening to the fucking going on on the otherside of the wall, Stiles hates Derek for being a good alpha.
Changing into a werewolf didn't change anyone's gender, it just brought all of them closer together at the worst possible time for Erica and Isaac. The two omegas in sudden close proximity to an alpha, all of their senses heightened, all of them reeking hormones and pheromones -- the bonding had apparently been epic. By the time Stiles came into the picture, Derek and his omegas had their routine down. When their heat starts, they come scratching at Derek's door, and he'll strip them, fuck them, knot them for hours, days, nights, as long as it takes.
And Stiles maybe hates that most of all because he's beta and as much as he loves Derek, as much as Derek says he loves him back, as much sex as they have, he'll never get the sex Erica's getting right now. He'll never feel Derek's knot or his frenzied power when he's swept up by omega heat. Stiles hates that he wants that, but fuck does he want it.
Boyd's in with them now. He and Erica started dating at the beginning of senior year, have already had beta sex, but tonight when Erica came begging so did Boyd. He can't give her what she needs, but he asked to be there. Derek of course didn't say no.
Stiles wonders if Boyd is just watching or if he's helping out. If he's got a hand in his pants or if he's as naked as they are, if he holding Erica's hand or fucking her mouth while Derek pounds into her. He doesn't know which one would be worse, so close yet still so far away. He just knows that worst of all is Derek telling him he's not welcome with them.
And he hates that he can't just walk away when they're all in the next room. He's already hard. When Erica starts moaning, gasping, "Harder, harder," and Derek's grunts change pitch, come faster, Stiles's lets his legs fall open, palms his dick through his jeans. He knows those grunts, knows the moment Derek's on the edge, losing control, shifting form as he slams into Erica rougher, harder than he slams into Stiles. He pushes down, feels the pulse of his cock, refuses to unzip against the building pressure. Those are his noises and he hates, hates that Erica gets to hear them, Isaac too, and now Boyd.
The noises on the other side of the wall rise into a fever pitch, and Derek lets out a long snarl while Erica gasps and gasps and gasps as his knot slams home and fills her. Stiles squeezes his dick, his ass clutching for the phantom pulse of Derek's cock, and comes in his pants, hating everything.
It's quiet now, but not over. Derek will be tied to Erica for a while, his broad body covering hers until he can pull away long enough for her heat to reassert itself, and then he'll fuck her again until she's raw, and Stiles will sit here, listening and hating every second of it.
He knows why Derek won't let him join them or even watch. Derek doesn't want anyone else touching him, or even thinking about touching him, because Stiles is his and his alone. What Derek doesn't get is that he belongs to Stiles, too.