I keep thinking about cheating

I keep thinking about cheating on my boyfriend. These thoughts almost consume me. It is a fantasy world that I live in. I write stories about it, and I try to find my old lovers online. I'm not sure if put in the actual situaition that I would have the heart to cheat. But I think that I might want to. Just to feel what kissing someone new or different is like again. The tingling from lips to toes feeling. The take my breath away feeling. So yeah, I'm a horrible person for having these thoughts. I have tried to talk to my boyfriend about it, and he even tells me that maybe I should go then. But that never happens.