What did Stiles do? If it happened nearly a year ago, is it worth holding on to?
As for Lydia, remember that it's not your responsibility to fix their relationship problems. Yes, it sucks if they're not talking and she's stressed, but you can't be the one to fix that.
Now, Allison. Surely she needs to understand your feelings on this. It's not just about you stopping her doing something, it's about her showing consideration for the things you've been through too. Also, just because her family did something, doesn't mean she has to. No offense, but you guys are practically still kids. Do kid stuff, study, think about college, let the people who have already done things like cynically destroy their livers with alcohol handle the monsters for a year or two.