Well some fantasies are just fantasies that happen when you get turned on. I for instance, have rape fantasies during masturbation. Of course I would never actually want to be raped, because the reality of it is awful. It's kind of like playing video games where you kill people. You have fun playing the game, but you'd never kill anyone in real life for obvious reasons. You have to ask yourself if you'd enjoy sex with a man in reality (when you're not horny) Think of it as realistically as possible. If the answer is yes, than feel free to continue experimentation. If not than it's simply a fantasy that helps you get off. Good Luck!