You've moved on why look back???????????
She hasn't moved on though, which is why she is discussing it in this forum.
You made the right choice, which I sense you know by your post. The problem you are feeling, as Sowrite has already stated, is that you have left some loose ends and you are not pleased with the way you handled the breakup. So maybe you don't need to give him the benefit of the doubt, but you need to give yourself some closure.
However, it is too late to reopen with him, and hopefully this sharing will be all the catharsis that you need. If not, write a letter expressing your thoughts, put it in an envelope, and put it into a drawer for a week. If you feel, after that time, that you have resolved your feelings, tear it up and move on. If not, send it to him without a return address.
Again, what you are feeling is about you and not him.