There's a part of Stiles that does consider himself Derek's. Not in a pack sense, at least not on purpose or in so many words, but there's a bond. He thinks it's friendship, at least potentially, something born of the innate trust you have to have to consider someone important. They've saved each other's lives often enough for it to be a thing. He trusts Derek, nearly implicitly, might even like his company just for its own sake if weird and life-threatening things ever stop happening. Like that's even a remote possibility. But is that pack? He doesn't know.

What he does know is that there's something off about Derek's words, something a part of him mind latches on to like a terrier with a bone as he turns the key in the ignition. "Wait, how would that make them safer? If they have to be out of the way first, in order for you to join up, then...I dunno. What exactly did Peter say?" There's something Derek isn't saying. Something he doesn't want to say. And that means Stiles has to hear it.