Relationship trouble.

I'm sorry if this is inappropriate for this thread, but I have basically nobody else to talk to about this, and nowhere to go for advice. I'm scared this problem will either end our relationship or contribute to it. Again, I'm sorry if I do or say something wrong.I've been with my boyfriend for about 5 years now, and we've lived together for four of those years. Generally speaking, we get along well - we have the same/similar interests in games, movies, shows, etc. We've been generally happy without a hiccup except for one. We had just moved in together and he and I both ended up cheating. In my case, I had two one night stands that he found out about by looking through my phone (shitty of me, I know) and in his case, he started cheating on me right around the time we moved in together (about 3-4 months afterward) and it went on for about a year and a bit. He found out about my cheating right before finals week of our third year of being together, so about a year and a half of living together. He was understandably upset and confronted me about it. When he did, I was angry at myself and wanted to leave. When I thought about the reasons I cheated, I came to the conclusion that I did so because I felt he was neglecting me physically. When I tried to initiate anything sexually with him, he would tell me he wasn't in the mood or he'd physically rebuff me. This went on for about a year and a half until my fuck up was revealed, then things cooled off even more between us.At the end of the year, about two weeks after he found out about my cheating, he went home to visit his parents for Christmas (he lived across the country from me) for a few weeks. When he was gone, I was cleaning the apartment and found a used condom in the bathroom garbage (which we almost never use because of cats). He and I have never used condoms before (firstly because I'm allergic to latex and secondly because he was my first, as I was his), and I immediately knew I hadn't been crazy about my intuition that he was up to something, and so I confronted him about it via Skype. He finally admitted to it and why he was rebuffing me made sense finally. Ironically, I felt better about myself physically because I knew then it wasn't an attractiveness thing.When he came back home, things were much better between us and we were pretty happy except for a few problems with one of the guys I messed around with. Those passed and that was that. How this all ties in with my current situation: I am mostly a bottom (75%-85% of the time) and I enjoy doing so. He claims he is versatile and enjoys both at near 50-50. Whenever it comes up that I want to top, however, something comes up or he makes a joke of it and flips me. The other day, I tried to initiate on him and he made a comment about how that's all I ever want to do. It seems small and he may have been joking, but I'm pretty sensitive about it because I'm shy and kind of insecure because of all the issues surrounding it. In any case, it seems to me he never wants to (the last time we did was over a month ago, and we've had sex 2-3 times per week since then with me bottoming exclusively during those times, and the last time I topped before that was three or four months prior), but when I confront him about it, it's always a huge fiasco because he insists he does. I'm afraid to bring up the subject again because I'm afraid I'll snap and leave.Thank you for sticking with me this far if you have, and I'm sorry for being so long winded but I felt a lot of background was necessary. Again, I'm really sorry if this is in the wrong place but I didn't know where else to go.