Could my boyfriend not be straight?

Hi,

I'm 25 yrs old, cisgender female, and do not consider myself to be bi or hetero, but I am attracted to both men and women. I have been in an 8 and a half year relationship, on and off, with my cisgender male, hetero boyfriend. Our relationship has not been easy since I discovered that my boyfriend has an unhealthy sexual addiction. We have been trying to work through it for almost 2 years now. Part of my boyfriend's issue is seeking "stuff", not necessarily sex, through craigslist, porn, chat sites, phone chats, etc. Back in March 2012, I looked through his emails and saw some exchanges between him and a male cross dresser. He had sent this person naked pictures of himself and from the conversation it seemed like he wanted to meet up with this other person for sex. But it never happened. When I found this I was devastated. I was already dealing with a lot of hurt from his cheating with cisgender women, and it scared me to think he was possibly doing this with men, or cross dressers. I admit it shocked me because this person presents male when they are not cross dressing, and all this time I knew my boyfriend as being straight. I never told him what I saw. I was embarrassed and didn't know how to approach the conversation. In my line of work, I work with a lot of people who are targeted because they are apart of the LGBTQ community, and I have heard their stories about being exposed or essentially being forced to come out. I have seen how it has affected their lives, and the trauma it creates. I didn't want to do this to him, so I kept quiet.

Back in November, I again discovered that he had been emailing people from Craigslist. He deleted the emails so I never saw what he sent but I had record of the email addresses and searched them on google. The posts were from transgender women who were listing places to meet them at glory holes. At this point I confronted him. I tried to be as calm and compassionate as I could and asked him to explain to me what was going on. I told him I would try my hardest to understand. Eventually he told me that he never intended to meet up with anyone and that he was just exchanging pictures of "those men who had boobs" (his words) because it was a loop hole. He thought it would be less of a betrayal to me. He has cheated on me with many women (that I know of) and said "boobs are boobs" but it was different because "they weren't women" (his words again). I asked him if he was gay or bi, but he said no. Even though I didn't believe him, I accepted it for what it was and tried to move on.

Today, on his kik messenger (which is something he agreed to delete and get rid of) under people he has recently conversed with was a transgender female. The picture was a naked picture of themselves. There was no conversation as I assume he deleted it. Again we talked about it but it was more of an argument this time. He denied ever talking to that person and claims they somehow found him. I asked him if he like men or trans people but he said no and he wasn't going to talk to me anymore about it. I finally brought up what I had discovered back in March and at first he denied it, but then moved to he wasn't going to talk about it. I told him I didn't know if I could do this anymore because I feel like he is lying to my face and hiding something from me that affects our relationship.

So my questions are...could he not be straight? And where do I go from here? I love him, there's no doubt about that, but I cannot fully commit to someone who is not fully committed to me, and by that I mean the infidelity and lying needs to stop.