A couple things come to mind.
First, I find the womanly form to be absolutely gorgeous. Not that I have a problem with the male body, but there is just something about the ladies that make it hard to keep your eyes off them.
Second would be that I have a strange attraction to lesbians. I don't mean in a sexual way, but that the girls I meet and whose company I enjoy tend to be gay. Not sure why it works out that way.
And finally, in my experience sexuality tends to be more of a spectrum than a gay, bi, or straight. You'd be surprised how many girls I have dated who identified themselves as gay beforehand. It's not always about genitals, but about the behavior and mindset we have come to expect from certain groups of people.