I don't think sexuality is a choice. I think recognizing your actual orientation is a choice (as stated earlier, many people choose to let society dictate what they should find attractive).
I thought I was straight until I was almost 18. My mom always wanted me to marry a nice Jewish boy and have two kids. However, there had been many signs that I was also attracted to women... As a basic example, when I first watched porn I thought the guys were all ugly and was mostly into the lesbian stuff. But I managed to ignore this for many years until a silly game of truth or dare made me start thinking about it. This realization didn't make me dislike men, but only that I can be attracted to women too. It hasn't been easy to be in a relationship with another girl, and my family and friends will treat me differently than when I've dated guys. Honestly, if I could control my brain I'd probably choose to be straight since it's so much easier. But as I cannot, I just accept it and find friends who like me for who I am.