I am a biaffectional who is generally more attracted to *men,* but I fell in love with and married a woman. Before my wife, the only other serious, very long-term (over a couple years) relationship I had was with a guy. I wish I could offer some insight, but for me it really hasn't been an issue or a struggle. I have never wanted an affectional relationship with more than one person. My dream life when I was a kid was not to have a small handful of husbands and wives. It was to fall in love with someone and get married and have a houseful of children. And here I am.
I find the intimacy and total focus of being in a "committed relationship" to one individual to be a very fulfilling and completely satisfactory. It helps that I have a very healthy, positive relationship and that I am very content with who my wife is. For me, her sex/gender really had nothing to do with it. I fell in love with *her,* for who she is. If she was the same person and a guy, I would have fallen in love with her as a guy. I do occassionally get crushes/feel attraction toward other people. That's normal. It's not like when we get married or come into a committed relationship that we turn certain feelings off, like an electrical switch. I just ride those feelings out, and I always feel like they were sorta silly when I look back a couple weeks later. There is only one person I can imagine being totally *perfect* for me, and that's my wife. I also know that I am an adrenaline-driven person and that I have a tendency to crave the excitement, the unknown, the thrill of a new relationship. Knowing this about myself helps me to keep those feelings in perspective, and it tells me what I need to do to keep my marriage happy and healthy.
I am remembering back to when I was with a guy, trying to think of something helpful about having an identity that isn't visible to the world. I do know that staying involved in my local queer-support group really helped because I felt connected to that part of myself. I wish I had something more useful to share.