When Stiles goes to college, for some reason, he has to share an apartment with Derek, which sucks, because Derek still hates him the most. They fall in love.

Stiles learns that even with werewolves, giant lizards and psychopathic hunters on the loose, life can still find other ways to screw with you. Case in point: everyone keeps assuming he and Derek are a couple. What the hell?

What it says on the tin. Canon-AU for Season 3 (obvs the finale hasn't aired yet so no real confirmation that it's canon-compliant)

Stiles would say his relationship with Derek is about fifteen percent empty threats, thirty percent sass, ten percent avoiding violence together, and five percent eyebrows. If anyone asked, he would say the remaining forty percent is mutual orgasms. It’s a good thing no one ever asks.

Pornstars Derek and Stiles work for the same company. Derek only shoots with werewolves and Stiles only shoots with humans. That's not going to change after they meet. It's really not. (It might.)