It has been noted that people with homosexual tendencies have, on average, a relatively greater caring for family and relatives than their heterosexual counterparts. They assist in carrying on their genes, not individually, but through their family members. By being more caring for family members, they increase their intrinsic survival over their darwinian survival. This evolutionary tactic is less effective then what is excepted as being "normal" but it is still effective enough for the trait to be maintained within the species. We must remember that evolution does not strive toward anything, it simply maintains whatever can maintain itself, no matter being "positive" or "negative".
Homosexuality indeed comes in various forms, but one of them is certainly genetic. Not due to one single "gay gene" but to a number of different factors that collaberate into one mutual effect. Either way you look at it, no matter how we think about it, there are people that are gay. They are, no matter what you tell them. I think the most important thing is not to condemn them, or look down on them. They are just people, leave them be.