AJLove, I'm assuming you want scientific evidence. Although that's not a necessary source of evidence for a lot of people, some people do need or want that type of evidence. Now, I'm not a scientist, but I do recollect that there have been studies of homosexual behavior in animals, and it seems to occur in the animals' natural environment. No precipitating event... just a naturally occurring way of expressing sexuality in the course of life for the animals (I'm thinking of the study involving mice... anyone feel free to correct me if I've mis-cited it).
And I believe there are ongoing studies about possible genetic insights into homosexuality in humans, but I'm not as familiar with those.
But I can also relate to the experiential side... it's just natural for me to be attracted to a woman. I can't tell you exactly why I don't want to have a relationship or even a sexual encounter with a man... and frankly I don't think I should have to explain why or why not. It just is. I just am attracted to women. Period. I wish we could let it rest at that. But unfortunately there are still so many skeptics out there, that people still need scientific evidence (and sometimes that's not enough!) to believe that homosexuality is okay.
-- "You must be the change you wish to see in the world."
-- Mohandas Gandhi