Am I crazy?

My boyfriend and I have been together for about a year and a half. We have lived together for almost a year now, even moved states together. Him being faithful was never an issue until we moved back to our home state. Even then it's only happened once, with his ex that he was with for 5 years before me. I don't know if it was just a moment of weakness or what. But we have talked about it he has apologized and everything like that. It just scares the crap out of me that it could happen again. One of our closest friends just cheated on his wife at the place we all work and I just don't want the same thing to happen to me. I love my boyfriend and he is the only person I really want to be with, and things have been good since we got everything in the open and talked about it. I just don't know if I am being a crazy person or not.