Am I a cheater?

Been with my boyfriend for two years now and have never orgasmed. It's my own fault because the feeling always gets too intense and I tell him to stop whatever he's doing. 
However, I'm curious about what sex with other people would be like. Of course, I've never acted upon these feelings but I keep having fantasies about other people. My boyfriend is so gentle and never is dominant in the bedroom, it's just not him. I'm having fantasies about a big tall guy throwing me around in the bedroom and my boyfriend is just too sweet. He would be so hurt if I ever voiced these feelings to him but I just don't know what to do.