It wouldn’t matter to me. I agree with betenoir, Aesiron, and sjc (and, on preview, Manda JO has a good point, too) – in fact, it frustrates me to see that there is still so much ignorance and prejudice regarding issues like this. I’ve responded to online personals where the man identified as bisexual: I see it as no different from identifying as straight, and I wouldn’t be any more or less careful about sleeping with him than I would with a straight man.
Of course there are some gay men who identify as bisexual to kind of ease themselves out of the closet. I’ve known a few, and am the daughter of one. But I also believe that true bisexuality exists, because I’ve known a few of them, too. I’ve found that the older the man is, the more accurate his self-identification becomes: I run into far fewer men in their 40s who are just calling themselves bisexual as a stop on the way to homosexuality than I did when I was dating men in their 20s. And a truly bisexual person is no more or less likely to be monogmous than anyone else – I reject the idea that a bisexual man will crave the cock that I can’t provide to the point where he would just have to go fuck a man or three. If people were only their sexual urges there would be no monogomy, period. But, of course, being bisexual doesn’t automatically make a guy a saint, either: the point is that he’s a person, not a sexual orientation.