Not being homosexual, it's not possible for me to know with any surety how one 'becomes a homosexual'. I have asked a few homosexual friends I've known over the years well enough to ask such questions, and their stories were quite similar.
They said they suspected something was different even as children, because they tended to identify more with kids of the opposite gender than with kids of their own gender. But that wasn't such a big issue for them, as kids are generally just kids, and gender identification wasn't something that they concerned themselves with.
When they reached puberty, however, they initially tried very hard to be like everyone else. They dated the opposite gender, and often had sex with them to make themselves feel, act, and be heterosexual. And it was the repeated failure of these attempts at being heterosexual that actually finally convinced them that they were not, and never would be.
Even the friend who identified as bisexual had this same basic childhood/adolescent experience, but ultimately concluded that he wasn't going to let gender define who he would be with (instead of concluding that he was simply "gay").
Since I am not gay, I have to assume that their stories are true (as I have no reason to doubt them), and that they are generally representative of other gay people's experiences. It was a very difficult struggle for those I spoke with to finally face and accept their sexual orientation as not being "normal", so I have a very difficult time believing that they chose this course just to disobey God or religion.