Science recognizes there are more chromosome combinations than only XX and XY, and thus there exist people with indeterminate genders, even if all that means is what parts they're born with. (I can't use some of the terms to describe them on the MB, however)
. . . "Polyamory means having multiple loving relationships, usually, but not always sexual. Unlike polygamy, people in polyamorous relationships stress the importance of open communication and equal relationships between partners whether male or female. Usually all parties involved know about the other partners and choose to be in those relationships."
I said bi people can be committed to one partner of X gender, but that doesn't mean they can't be attracted to Y gender later. Just like straight people - Y can be committed to a relationship with someone of X gender, but that doesn't mean they can't get attracted to another person of X gender, they just should not act on it.
Also, if nobody is getting harmed, I don't think it's my business to care about how many partners one has :)
Refer to Sassy's answer about aro/ace :) Couldn't have said it better.
Some other stuff I found on the internet while doing my research was the Genderbread Man, which was pretty interesting.
In case anyone thinks I have biased search terms, this is what I looked up -
"How many genders are there?"
"Polygamy vs. polyamory"