Scott
I don't really know if there is a way to explain it. I just understand where Stiles is coming from. Sometimes saving someone is more important than anything, including your own life and even more than their feelings.
Because most people snap under stress for too long. Bottling things up, trying to push on until finally, boom. It might be an internal boom that you inflict on yourself, or an external one where you lash out at others, who knows. But eventually, boom.