I'm a guy. I like girls and only girls. Sometimes I like to change into women's clothes.

But I've had a fantasy for a long time where I imagine myself as a girl being fucked by a tall athletic guy with his huge cock. There is no face in these fantasies.

I've had this experience and it was just disgusting and rather traumatizing.

When I'm in a relationship these fantasies never come up. But when I'm not in a relationship, this fantasy comes up periodically. I'm clearly aware that I'm not attracted to the guys themselves, but these attributes - big dick, tall stature, athletic body - enhance femininity and so on.

But why does this happen?