The American Psychological Association, American Psychiatric Association, and National Association of Social Workers stated in 2006:
“ Currently, there is no scientific consensus about the specific factors that cause an individual to become heterosexual, homosexual, or bisexual—including possible biological, psychological, or social effects of the parents' sexual orientation. However, the available evidence indicates that the vast majority of lesbian and gay adults were raised by heterosexual parents and the vast majority of children raised by lesbian and gay parents eventually grow up to be heterosexual.[2]
I remember watching a documentary a few years back about a pair of identical twins, raised with the same DNA in the same environment, but one was gay and the other was not. One of the suggestions they came up with was that both of them had the 'gay gene', but it only activated in one of them.
If we're talking environmental factors, the way we were raised has little effect. I suspect that the way these factors affect our sexuality is haphazard enough to be random, or subtle enough to go unnoticed. For example, in the potential reasons you posited for your own heterosexuality I could agree to pretty much all of them myself. My first pre-pubescent crush was a girl, and my second too. It wasn't until sexual attraction came into play that I turned to guys. I was exposed to just as many images of women, after all they tend to be more often objectified by the various media we have around. There's a stereotype played up by the other side that overbearing mothers, distant fathers, an abundance of female friends, and an interest feminine things lead someone to turn gay. My parents were both there, neither overbearing nor distant, during my teenage years I had no female friends at all, and my biggest interests have always been video games, science fiction and books, non of which are typically feminine.
I could accept the idea that I possessed a gay gene that was activated instance of random chance. But there was nothing in my childhood that was different from my straight brother, or my straight friends.
It's also interesting to note, as no one has brought this up yet, that the more kids you have, the more likely one will be gay. And it's not just probability, as it is the youngest is who is most likely. Current theory, I believe, implies this is nature's 'limiter'. Alas, with seven billion on our planet and growing, it isn't working.
