First, I think you should give her some space if you haven't already done so, so she can clear her head. You should also do the same thing and not dwell on her so much or you'll drive yourself insane. Secondly, when you talked about changing, you need to think about whether you're doing it for the right reasons. As you mentioned, she probably thinks the same issues/problems will come up again that split you two in the first place. Therefore, if you change for the wrong reasons, the relationship will be short lived again. When you do change your behaviour it will take dedication. You will need to set small, attainable goals that can allow you to move forward. But most of all, you need to be happy with yourself. If you're having doubts about changing, you should take a step back and rethink what you really want.