Please don't have a nasty taste in your mouth about poly, what you experienced was not poly's fault, it was your bf's fault and the woman he chose to be with... not to mention the situation.
No kidding you don't trust him! He cheated and lied to you... that is not good poly practice. Just because you knew he was seeing her does not mean that it wasn't cheating. He cheated because he had sex with her when you asked him not to AND HE AGREED NOT TO.
Poly is about building a foundation of honesty, respect, integrity and communication, of which he fell flat. To me, if I find myself in a situation where I will not have one of those four things, then I won't do it; because it jeopardizes the foundation I have built.
You both seem to have a lot of work to do to take what you have learned and use it for next time. I would wonder if he has cheated on you or someone else before. The fact that he was so easily swayed to go with his cock over his head is a red flag to me. The thing with cheating and casual sex I have found is that it is easy to sexualize a relationship when there is no call for it and it isn't appropriate. Perhaps this is what is going on for him?
Anyone want to be friends on Facebook?
Send me your name via PM