There was an interesting clip on 60 minutes about this. They are doing a study on children and their behavior. How they dress, what kinds of toys they like, their movements, etc. They studied several videotapes of adults when they were children and asked people to guess whether or not they are gay. Many people were correct when they picked out the child that is now a gay adult. They showed two twins (boys), one had the military room with G.I. joes, etc. the other had a somewhat feminine room with ponies, and pink stuff (he even had on nail polish).
I don't think its a learned behavior or lifestyle choice. Two girls dancing and kissing each other at a bar to get attention, is a choice. Having feelings and sexual attraction for someone (regardless of sex) isn't. I'm probably wrong, but, I just don't think its a "choice."