I would point out that the nature / nurture debate has nothing to do with the "choice" debate... nurture does not mean "choice", it just means that the psychology is shaped by early experiences. It's no more of a "choice" though... just as (for example, I'm not making a direct comparison!) a phobia is almost always rooted in early childhood, but is certainly not a choice... it's as ingrained as any instinct.
So anyway, away from the nature/nurture debate, whichever it is, I certainly don't believe that it's a choice. One of my best friends, who I've known for almost 15 years, is gay and quite "obviously" gay. Not an Alan Carr or a Rylan level of obvious, but at least a Graham Norton on the scale. You can tell, basically. Anyway - myself and basically all of his close friends were CERTAIN that he was gay, from when we were around 14. Like I said it was just obvious! We brought it up with him several times and he said he wasn't. I once even pushed the issue by asking if he fancied anyone in our year, and he really did try... bless him... to pretend that he did. When I asked what he liked about her, he said she's "just really nice".
He kept up this pretense for years (we didn't constantly badger him about it, just occasional comments like "yes but that's because you're obvz gay..." which he would laugh off) and didn't actually "come out" until we were 19 and at University. He did it like a big reveal at the pub, as if it would be a shock, it was brilliant.
"Guys.. I have something I need to tell you all..."
"Is it that you're gay?"
"...yes..."
"FINALLY!!!"
OK so I'm rambling a bit - but anyway, the point is, we knew he was gay before he was ready to say it to anyone or even admit it to himself properly. For FIVE YEARS. So we knew that he WAS gay before he ever made the "choice" to be openly gay / start any sort of homosexual relationship. So saying that it's a "choice" makes no sense. If that was the case, no one would have noticed any "gay traits" until he "chose it". Surely.