While there are many choices that all people make in the sphere of sexuality, choosing who lights your fire is not one of them. I can no more choose to find men sexually attractive than I can choose to not find sugar sweet.
I have no way to answer that without resorting to anecdotal evidence, as you are yourself doing. I could answer with quotes from the "ex-gay" movement ... but those are anecdotal as well.
I don't think there is a way to gather hard evidence without engaging in unethical conduct (that is, any psych experiment that would give data might irreparably harm people and thus would be wrong).
