I do not think that we choose who we are attracted to. I believe it is a combination of factors that determine what we personally find attractive. However I do believe that our behavior is a choice. If we chose to engage in heterosexuality or Homosexuality or no sex at all it is a choice. We are all responsible for our own behavior.
I agree in part with what you've said. There have been several times I was with a great guy, but the
"chemistry" wasn't right. I also teach with a great teacher now, we co-teach very well together, because we have "chemistry", but neither one of us would ever act on it.
However, my sexuality was not a choice, other than my choosing to have sex. When my daughter was young, and I watched her at play...I know that sexuality and gender start extremely young. My daughter loved flowers, and butterflies, and princesses...and now, she likes One Direction because they're "cute". There was a little girl in her class, even that young, 3 or 4, that gravitated towards girls...kissing them, hugging them, patting them... tell me how that is a choice?