He’s not gay. He’s bi.
True (male) homosexuals don’t create children, except through artificial insemination. He can clearly get it up for a woman, even if he may prefer men.
I don’t have a “preference” myself. The word preference implies that one can go either way, just that one is better than the other. Given a choice between a man and Rosie Palms, I’ll take the latter every single time.