I guess that, even though the question is “guys how do you feel…?” the real issues here are two:
1. Should the bisexual (woman) tell?
2. How do/should the boyfriend react?
So Alive is actually answering the first question, and I also agree that, even though there is no need to tell people everything on the first date, mentioning your sexual preferences (which are part of your personality) is the basis of a healthy relationship.
As far as the second question is concerned, I think it was laureth (as well as daloon) who mentioned this already: liking men doesn’t mean she’s going to cheat on you with another man, so liking women doesn’t mean she’s going to cheat on you with another woman. Who was it that mentioned liking two types of hair? Bisexual, homosexual and heterosexual people all have exactly the same chances of being cheaters, and it is not important WHO they will cheat on you with, but WHY. I don’t think that, should my gf cheat on me, it would matter much whether it was a man, a woman or an amoeba for that matter.