Stiles has a magical thingamajig that's supposed to get him out of danger. Trouble is, it took him really, really far out of danger. Like, to the point where he isn't in the same universe anymore.
"A part of Stiles had been thinking that he’d come home, and just go, 'hey, Derek, are we mates and you just haven’t said anything about it?' and Derek would reply, 'now you mention it, we are indeed! Now come to my bedchamber, where we will have super hot sex and then cuddle after!'"
- Part 1 of Parallels
Stiles doesn't know the name of the man, just that he needs him like breathing. Apparently Stiles has been drowning this whole time and he's only just found air.
(Companion to Where The Inevitable Isn't but you don't have to have read that.)
- Part 2 of Parallels