Did I do something wrong?

My Ex broke up with me a while ago, and I think hes the first guy I ever really, REALLY liked, and I can't get over him!
I tried to be there whenevrr he was there for me, he made me feel safe and welcome, but he told me he wasnt ready to commit to a relationship.

I know it seems petty, but I'm just upset over it, I feel like it was somehow my fault, I did something wrong .. I'm gonna be at a party where he's at, should I bring it up with him? We're still friends and talk normally, all of my firends just say to ask him but I'm scared, terrified, really, I just want to be with him again, is that so bad?
What should I do ..?