I think one's position on the sexual orientation spectrum is predetermined, but I do agree that, just like with gender identity, we can force ourselves, consciously or subconsciously, to conform to external influences. For me, the acid test of sexual orientation is the involuntary arousal response that is invoked during a sexual experience. In other words...what turns you on?
I remember years ago I was on a business trip and staying at a hotel. One evening when little else was happening to divert my attention, I called up an adult movie and settled in to watch. There were a couple of beautiful blond women in a bath tub together enjoying their bath and each other.
I experienced the normal arousal response that seeing a woman's beautiful body normally induces. Then, both women stand to get out of the tub and it's revealed that they are T-girls! Well, let me just say, that I never knew arousal like I experienced arousal at that moment. It was the day I learned that I was attracted to convincingly feminine T-girls. 
Now that was my T-laden male persona's response. Clara is a T-gal herself, and that puts a different slant on things.
Clara
I remember years ago I was on a business trip and staying at a hotel. One evening when little else was happening to divert my attention, I called up an adult movie and settled in to watch. There were a couple of beautiful blond women in a bath tub together enjoying their bath and each other.
I experienced the normal arousal response that seeing a woman's beautiful body normally induces. Then, both women stand to get out of the tub and it's revealed that they are T-girls! Well, let me just say, that I never knew arousal like I experienced arousal at that moment. It was the day I learned that I was attracted to convincingly feminine T-girls. Now that was my T-laden male persona's response. Clara is a T-gal herself, and that puts a different slant on things.
Clara