How do I Move Past The Cheating?

OK so here is the thing, My BF and I have been together for almost 9 months we love each other and feel like we are meant to be. I found out 3 days ago that he has been cheating on me since December with one of his Ex's that i did not know about. She had no idea he had a serious GF until i called when i heard a msg she left on his VM, she said had she know she never would have started to see him again. It is a really messed up situation that involves controlling on my part and feel smothered on his and lost of previous history and emotions. The bottom line is that we love each other and we want to try to work through this, but i am just wondering how you work past something like this, is it true once a cheater always am i totally stupid for trying to get past this? I always said i would never put up with cheating but i have never been in this situation before it is always interesting how you say you will react and how you react when something happens to you. Anyways please help right now he is committed to making this work and giving me the space and time I need but i need you guys to help me....thanks xoxxo Squishy