[afc wimbledon]

I am not sure the existance of a trait means it bestows an advantage.
Many traits have died out because they didn't bestow an advantage, but they existed before hand, food alergies exist, but do not appear to be anything but a disadvantge and in the natural order of things will eventually die out.

That said being gay does not mean you cannot procreate with a woman and many societies that developed along predominantly same sex lines (classical Greek etc) still managed to retain marrige for the purpose of breeding.
I think very few gay men don't have some sexual experiances with women in their lives, Graham Chapman of Monty Python described driving in a cab and realising that he was attracted to 5 men and 2 women as they drove down the street and as such he decided he was gay.

As long as we have booze men will manage to shag women they arn't attracted to that much, whether that is due to same sex preference or the general fugliness of the bird is really neither here nor there.