Being bi is stepping stone to admitting your gay?

A lot of people say that being bi is just a stepping stone to being gay. I know I'm bi but are kinda sorta questioning that and a gay friend of mine asked me some personal questions, you know just doing a little digging and he says that he truly believes that I'm gay and just have been REALLY suppressing it. He says he started bi too. But that's neither here or there. What do you guys think of this theory in general?