Gay male chiming in here with some blunt honesty.
Keep in mind that this is my opinion, based on my experiences, and not backed up by any statistics or objective criteria. It is, in other words, a prejudice.
I know bi people exist; I’ve had sex with some of them. I completely believe that people can be attracted to both sexes. I believe that they can be faithful in a monogamous relationship. I don’t think that being bi makes you promiscuous, or flighty.
But…
I’d think twice about having a serious, long-term relationship with a man who identified as bi. I wouldn’t rule it out altogether, but it would count as a strike against him in my book.
Why? I think it boils down to insecurity on my part, but let me explain. Think of it as a scale. On the one side, there’s me. On the other side, there’s a Woman Who Is Yet To Be Identified. There’s also kids. A legal marriage, and all that goes with that. Walking hand in hand in public, without a single worry about safety. A better chance at parental approval. A life that falls comfortably within the bounds of societal convention.
And on the other side of the scale, it’s still just me. Now, maybe I can love him better than the WWIYTBI. Maybe I can make him happier than he’s ever been. But, to my way of thinking, I don’t have much of a chance when competing against the WWIYTBI, plus all of the attendant advantages of heterosexual life. I just don’t feel like I can compete with that. It feels like an enormous amount of pressure; I don’t just have to keep him happier than he would be with someone else, I have to keep him happier than he would be if he was in a heterosexual relationship, with all the societal trimmings.
I’d have a hard time believing that, no matter how good we were together, he’d eventually wind up in a straight relationship. There’s a lot of crap to put up with if you’re gay in these here parts. I can’t imagine anyone dealing with all of it, permanently, if they had other options.