How do you deal with unwanted same sex fantasies (NSFW)?

I have a very good relationship with my boyfriend, but lately I cannot get the thought of sleeping with a woman out of my head. My boyfriend isn’t the type of guy who wants a threesome or to share me with anyone, which at least he is more fair than the average guy I know. But these thoughts are driving me bananas. I don’t feel comfortable telling most people I know about these fantasies, even when I am single. Sometimes I am scared I am more into women than my own boyfriend. Sometimes when we make love, I can only get off if I am thinking of another woman…. he is not doing anything wrong. And he is great in bed with me. I don’t know how to deal with these feelings, and what it means.

How can I control my thoughts so that I think of my boyfriend instead of another woman when we make love?