If you're born a guy, you're a guy. If you're born a gal, you're a gal. If you are naturally one gender, that means, no matter what happens to you know what, (no more detail.) you were still born that gender. Then... You are gay. (LOL I wrote gay and typed wrong... And it said fat.)
If you changed gender, say from female to male and you are now attracted to males, then you would identify as a man who was gay. Visa versa, this isn't a debate question, this is a Google question. And to the commenter up above, gender and sex are two very different things. Both of which can change in ones lifetime.