Well, sexuality isn't black or white. There's a whole spectrum, not just straight, bi or gay. My wife for example is a little bit bi-curious. She likes watching two women together, but would never consider actually being with a woman.

It sounds like you are like this yourself. Don't worry about it and don't worry about trying to force yourself into nice little category. There's something you like about the male anatomy at a fantasy level and that's just fine.