What makes polyamory illegal? Are you in the US?
Also, not wanting a lot out of someone aside, you're putting expectations in an area of a relationship that varies a great deal. I worry you're lack of communication skills would make things unclear to a new partner what it is you're truly looking for.
And I'm still worried about your boyfriend's marriage. He's having an affair, and you're half of that. Understand that love is a powerful thing, and your loving this man IS affecting his marriage. Consider his predicament, and his wife's feelings.
What makes you think you're bipolar? And how impulsive are you about your sexual actions? If you did have a mental disorder, would you simply point the finger to that and state that it's the fault of a condition, or are you willing to work on yourself instead? Stable relationships start with the person in the mirror, my friend.
Again, pardon my blunt shortness here, but I don't think you're looking past your own needs far enough to be able to handle this gracefully. Here's what I would do if I were you:
End the relationship with your current boyfriend. I want to love others, but in doing so, I don't want to hurt anyone so I will avoid doing so as best I can. Ruining someone's marriage by engaging in an affair could definitely hurt a couple people, which makes it worse because it's a totally preventable scenario. I'd sit down and think about what I want out of a relationship. Are those wants likely to be compatible with other peoples' wants? Why or why not? When I met someone I liked well enough, and if they seemed interested in my romantically, I'd make it very clear what my wants were, and that I was POLYAMOROUS, and before even holding hands I'd make sure they were comfortable with that. If not, then I'd keep things at friend level, and enjoy that individual as best I can there. Fish in the sea and what not.
It's direly important that you look at yourself and be truthful with you. Self criticism is paramount when wanting to be with other people, poly or not. If you can't do that, then how can you work through inevitable arguments and disagreements without going into "victim mode" and pointing the finger at everyone and everything but yourself?
A book I recommend for you is called "The Ethical Slut". You may have heard of it in passing around here. It has some keen advice on how one should conduct themselves in poly situations.