Myth number one is that bisexuality is only a transition phase for people who are coming out as gay or lesbian. And I've got some realities written up on the back here. It is true that some gay or lesbian people go through a stage when they identify as bisexual. Many people feel that is a safe stopping point on the way to a gay or lesbian identity. It is also true there are people in the community who identify as gay or lesbian from the moment they came out, and then later on discovered that they felt bisexual and came out about as bi.
Many people identify as bisexual for their entire life.
And for some people, the experience of their own sexuality is fluid. It can change over time. My personal experience is that my sexuality has stayed pretty much the same, but the way I think about it has changed over time. So that coming out as bisexual meant to me reconciling all the different pieces of my sexuality. Bisexuals are equally attracted to men and women.