I agree with everything you've said so far but think that homosexuality is more of a psychological thing than physical still. That said i don't think it's a choice...it's obvious that it's not a choice, you can't choose what you're attracted to.
Like you said, i don't think it's genetic, i think it's just learned behaviour like all attraction is really. I'm more attracted to women with nice toned calves and prefer brunettes over blondes but it's just a psychological thing really, none of that was in my genes. All that's in my genes is how my body was developed. I learnt how to behave from my environment when i grew up.