Totally off balance

I really don't know which way to turn. I lived with this guy for almost 5 yrs..drugs and alcohol caused us to break up and the fact he stopped sleeping with me. He gave me every excuse in the book. So I left him. It's been two years since we have been together, although we have continued to talk, there has been no physical contact. i honestly believed him when he said he had no sexual drive. He recently told me he wanted to work on getting back together, and I am considering it. Here's the catch, I just found out he had been having sex with his neighbor. I'm not upset about that, I haven't been an angel either, but I can't help but wonder why? Why have sex with someone else and not me? I'm so confused.

you must ask this question to him ,you need to.