Let me start off by saying this: I love my boyfriend. I've written countless songs about being madly in love with him. But I feel differently about my attraction to him as soon as I get especially horny (around ovulation). I don't want to be anywhere near him during this time because I picture myself with a girl when we do things. I wish I could feel what he feels when he touches me. He's got especially soft skin but it doesn't feel... right. I feel intense shame and guilt for having these thoughts. He knows that I fancy girls but I don't think he REALLY understands the torture I put myself through every single day.
I can understand. I think it's sometimes easier to accept a same-sex sexual attraction or fantasy than the concept of being in a same-sex relationship, especially for people who are questioning their sexuality. In your case, it could be that you're attracted to men only romantically (not sexually). However, if you don't find yourself sexually attracted to your boyfriend or men at all, I would probably reconsider your relationship if I were you, it wouldn't be fair to the both of you. Both of you guys deserve to be happy.