Currently Online 
First, I think, we have to entertain the idea that all homosexual people are not created equal. What I mean by that is perhaps there are different roads to the same destination. Perhaps there are gay people who born that way, some who end up that way from environmental factors, and some who get there by some degree of unconscious choice.
The reason I believe the last exists is from personal experience. Someone I've known since we were kids ended up being gay. Except, honestly, I don't think he was to start with. I remember him being hopelessly besotted with two different girls, neither of which worked out at all. One basically used him and the other was an unrequited love he harbored for years. He was pretty emo, and arrogant on top of that, so he kind of retreated into this "I'm different from everyone else" frame of mind, where he imagined himself as gifted and special. In fact, he adopted a homosexual artist as his idol. Still, at that point, I think he would have just considered himself bi-sexual or something like that, but a college professor known for having affairs with both boys and girls put the moves on him.
Now, you might be thinking that the last part is supposition, but A) he told me about their affair, and B) awhile later, the same professor tried to pressure me into ... stuff. He kept finding reasons to get me into his office for talks. He flattered me and told me how smart I was, then he would bring up his views on sexuality and how love should be free and open. He talked himself up, told me that he was the smartest person I would ever meet (honestly), then asked me if I was attracted to him, because he was attracted to me. I avoided the absolute hell out of him after that. Not because he was bi-sexual, but because he was obviously trying to pressure students into sex, which I think makes him a scumbag. I'm sure he saw me as an easy mark because I was quiet and not very social, just as he saw my friend as an easy mark for being gullible and susceptible to flattery.
Obviously, none of that is proof, but it's something I believe. I'm almost certain environmental factors, as well as a conscious direction, were big reasons why he considers himself gay now. Never mind his overbearing, overprotective mother who spoiled him and controlled his life completely.
As far as the questions in the OP, sexual association is -extremely- powerful. Conditioning probably could take care of the first two questions.
