[Jack_]

For the most part humans are born as blank slates and every inch of our personalities and mannerisms are learned, socialised behaviour. This includes sexuality, and gender.

That is not to say that you ~choose~ your sexuality, or that it can be changed, this is a common misconception people seem to have with the nurture argument. I don't believe that you are born gay (or straight or otherwise for that matter, sexuality is a spectrum that individuals fall upon somewhere in the early developmental stages of their life), but that doesn't mean I think that people choose to be gay (because like people have already said, you just wouldn't) or that you can change your sexuality, because you can't.