Thin Ice: On sexual inclination

Before we begin: I know I'm on thin ice with the following subject and I debated tossing the question up on Quora or something like it, but I'm not looking for the opinions that come from behind the mask of anonimity.
Also, I'm not trying to troll and if this thread slips out of control I trust that someone will kill it off.

Now, the question, put bluntly:
Can you choose to be gay?

I ask this because the argument came up in my story and I am close to someone IRL who, due to incidents when she was younger, does not care for sleeping with men anymore.
The more I read about it, the worse my grasp of 'being gay' becomes. In the case of my question, I would define 'gay' as intercourse with someone of the same gender. Though I would add that this is not necessarily my personal definition, since I'm not even sure if it can be defined.
The reason I am confused about this is that as far as I've been told, you either are gay or you aren't. The 'born this way' principle, I guess. So if you could choose to be gay, would that even count? So to speak.

Summing it up: Supposing something traumatic happens at the hands of one gender, could that turn a person to stick with their own gender? And have they then 'chosen to be gay'?
And, assuming this thread will be troublesome enough, let's not get into the implications of undoing that choice.

In closing, since it'll probably come up at some point:
If you haven't figured it out already, I'm straight and I firmly believe I do not need to have an opinion on someone else's preferences.
In fact, considering my first love was Queen and not much later Judas Priest, I'd be a right hypocrite if I did.