Bisexuality does not equal polygamy. Bisexuality is not two sexualities. It is merely the ability to fall in love or lust with either a man or a woman. Bisexuality removes the requirement of gender in one's choosing of a mate.
Now, sometimes, I'm sure that one might have a craving for a guy one night, and maybe a craving for a female another night. But, that is no different to me then, some nights I might crave a black guy my age, and maybe the next night I crave a white guy who is older; or maybe one night I am craving a red headed guy, the next I am craving a brunette.
I might even fall in love with two different guys (much like on the Bachelorette lol). But on deciding who to marry--I have to choose that one human being that is to be my partner.
It also sounds like (and please forgive me if I read your post wrong) you gave up on the female because you couldn't get married and have kids. Well, then you must not really have been in love with her or your need for "marriage and kids" is greater than your need for a partner, thus choosing a man. But, then you have to ask yourself--do I really love this man, or is he just giving me what I need?
And, I include bisexuals (as well as trangendered) whenever I say "gays". I fight for equal rights in marriage and all things pertaining to sexual orientation to protect heterosexuals as well. Because, in many ways, this all boils down to gender issues and removing the labels. All AMERICANS should be treated equally and regarded as AMERICANS, not these other labels.
I, personally, do not find polygamy offensive--to each his own. But, right now, the issue being fought is for two people to have the right to marry each other---including the right for a bisexual to marry same sex if that is who they fell for. If polygamists want to fight for that right, then they can take that step one day.