Turns out you're not born that way:http://sourcefednews.com/theres-no-gay-gene-says-scientists/
This is more or less what I thought to begin with, so I'm not too surprised. Although, I was starting to get comfortable with the idea of being born with it. I don't think it really changes anything one way or another, even if it can be proven 100%, but it's worth a read.
Full study if you want to read it for some reason: http://www.jstor.org/stable/pdfplus/10.1086/668167.pdf?acceptTC=true