I never felt like it was something I had to "admit", it's just who I am.
I still find it funny how a lot of people assume you're straight when you don't say anything, but they expect you to knock on their door and lay your cards on the table unasked when you're bi or gay.
So that's not what I did.. if people don't ask, why tell?
Just two exceptions to that rule:
1. Do talk to someone you feel comfortable with if you feel the need
2. Let any potential same-sex partner know, or you'll only be bi on paper