It's your past, you decide what to do with your secret. We all have them..plus it's a private matter that only when you feel secure enough with someone, you'll share. I do agree though that once you find someone you love and you think they're the one, tell them before you take a step further.
Still, when I hear stories of people feeling "betrayed" once they learn a close friend or bf/gf are transsexual, I find it ridiculous. I don't see at what point must I point out "oh look, I'm transsexual, I was born a female, so you shouldn't be attracted to me or befriend me because of my birth condition, I'm not "normal" or what you consider normal at least" if I do get to the point in telling you, is because I believe I can trust you enough and like you enough to let you in, I expect you to feel honored, it's a rare thing I personally would do.
It's not being ashamed of being transsexual, I just believe that people need to stop so self-centered and ignorant and stop judging others based on what makes them different. I wouldn't judge you base on your race, height, gender, sexual orientation or disabilities, so why should you judge me before you get to fully see the real "me"
Man, our generation needs to change what our past generation couldn't change.