I am a 33-year-old gay man and I am currently dating a man of the same age who identifies as bisexual. He is attractive, and I enjoy our sex life, but I have worries. When we go out to dinner, he will frequently flirt with the waitress or other women in a way encouraged to make them think he is available, even though he is sitting with me. He will not act romantic until we get to a gay bar. Of course, I wouldn't like it if he flirted with other men either but I notice he never seems to do this, just women. I find it distinctly uncomfortable and wonder if he is capable of sustaining a relationship with another male.
To be blunt, probably not. I won't even get into whether or not this guy is actually bisexual or what his preference is, but it definitely sounds like he is dealing -- and not at all well-- with internalized homophobia. I will just say that a lot of men who are embarrassed to be gay/bi and full of shame need to have women in their lives even if only as a beard or front. They have to exude some kind of heterosexual persona even when they're out with another man. The fact that he flirts with women but never men indicates that he is uncomfortable being out in public with a man except when he is in an all-gay environment like a gay bar. I have no doubt that he is the kind of "bisexual" who tells gay men he likes women but never tells the women whom he gets involved with, if any, that he also digs guys.
Frankly, as far as I'm concerned that is not being bisexual, it is being a closet case.
Your friend needs some counseling and a good dose of gay pride, but you have to accept that for one reason or another he may never feel comfortable in his own skin. Just the very idea of his hitting on women when he's on a date with you is rude and insulting and a little outrageous. And desperate. Like he's trying to prove something to himself.
My advice. Fuck 'im and forget 'im!