I was in your shoes during high school, same drama... Years later I found out had I asked her out she would have said yes!

OP, answer me, do you believe that you could make her happy? Do you think that you could be there for her when she needs you in the future? If you said yes, then why not go for it? You can't let the classic dilemma of "If I ask my friend out, it'll ruin the relationship" ruin what could be beautiful. This could honestly be your chance, and I while I was thinking... WHY DIDN'T YOU SAY "I could be that guy" when she said that in her apt!?

OP, what hurts more?
Asking her out and failing?
-or-
Burrying your feelings again, watching from the sidelines while you watch her be taken by another guy, and deeply regretting it?

Seriously, if you're as good as friends as you guys say you are then if she happens to say no, wouldn't you guys be able to get past it?

Just go for it. Sheesh!