Somehow missed this thread til now but I see it's full of the usual biphobia.
To be clear, "biphobia" doesn't refer to anyone's individual dating preferences, but to how they're expressed - the vocal disgust, repulsion and insinuations that it makes men less manly.
We all have preferences and that's OK. I'm not attracted to overweight men or ginger men. I even have a racial preference in terms of pure sexual attraction. I keep all those to myself, I certainly don't frame any of them in terms of disgust, and I choose my partners accordingly.
Biphobia also refers to the scenario in which discovering your partner's bisexuality would be enough to undo many years of loving them and being in a relationship with them. The idea that it's so disgusting that it overrides everything you love about them as a person. And it's illogical, because bisexuality is not something that's evident in either someone's appearance or their behaviour towards you.
In many cases the biphobia isn't even about bisexuality but bicuriosity and the idea that a straight man might have experimented with another man in the past (much more commonplace than you think it is).
Personally I'm happy to date bisexual men, am attracted to the idea of two men together, and in my experience have found that the kind of man who's secure in either his bisexuality or his openness to experimentation is also the kind of man who's free from a lot of bullshit hang-ups about masculinity. Win-win.