I'm Bisexual, and have been around a lot of friends and people that are of pretty much every orientation. Even when I actively played an online game, I recall meeting someone through voice chat that was born male, and you could hear the male voice, but believed that at heart, he was a she. Had a gender change to go with it. One of the nicest people I'd met, but sadly emotionally scarred due to society.
I noticed the topic has brought up whether it's born or choice. I personally believed it was choice at first, but as time went on, people began saying it was scientifically proven that it is in fact, something you're born with through genetics. So one day, I started probing questions at my parents, if they'd ever been attracted to the opposite gender in any way throughout their lives. My mom, I was sure was straight, and her answers came off as just that. My dad however, had been in prison most of my life so I didn't grow up with him or have any kind of intuition on his orientation. So I probed questions at him, come to find out he's had a history with males and considers himself bi, but because of his upbringing and his strict parents, he wasn't one to talk about those things. He was adopted, so his parents were straight, strict, and conservative.
Sure this isn't a full scientific explanation about whether it's a choice or if you're born with it, however, if in fact I was born with it, then I know I have a piece of the puzzle to support that thought.