Stiles opens his mouth a few times, but no words come out as he feels tears welling up again. He takes a deep, shaky breath, exhales slowly to calm himself enough to do this. Peter waits, brows furrowed in worry as he watches Stiles. “I think I’m pregnant,” he finally says, “And I don’t know what to do.” -- Or the one where Stiles is a human incubator and Peter is not the baby daddy (until he is).
Stiles asked Derek to be his heat partner and quickly lost track of him. Now Stiles is pregnant and alone, but when he goes looking for Derek he finds something else entirely.
For Peter, it's practically love at first sight. He just has to get past Stiles's defenses.