Do you become gay or is someone born that way?

Born that way. It is interesting that those who say you choose that are not scientists - they are radical priests or politicians. Multiple scientific studies have shown that it is not a choice but something wired in you. There have even been studies on brain imaging to show this to be the case.
Born that way. The evidence is pretty clear that by birth our sexuality has been determined. While this continues to be a source of controversy in the political arena, overwhelming scientific evidence indicates that male sexuality is determined by genetics and the intrauterine environment before birth.