Really tough position to be in a relationship.

My boyfriend and I have been together for two years. I started to find out as our relationship progressed that he was really unfaithful towards the beginning of our relationship. A lot of different incidents that are definitely considered cheating. He says he's changed and has shown me that he has. I really don't think he's doing anything now and our relationship is good. But honestly getting over that kind of hurt is proving to be so difficult for me. I love him so much but I find myself thinking of the things he did a lot even though they're almost two years back. My biggest fear is to be clueless again. Because honestly when he was doing it all I had NO idea and I would have never though it. Have any of you ladies been through a similar situation? Do you think things like this are fixable or something that will always be broken?