I'm wondering how much communication is going on here. That and what kind of arrangements have you made with him? It sounds by what you've said that he has said he is poly and that means he can do what the hell he wants; not talk to you about his feelings openly and honestly, not respect yours or what your nature is, not act with integrity and does not have compasion for your position and point of view.
I agree that his behaviour sounds more like cheating and using poly as a means to make it okay. Being honest about who you sleep with does not make you poly as far as I am concerned. Its more open cheating.
Not that you have to completely have total control either. Giving *permission* for him to do things is controlling to me and not respecting him in return. If you want respect, you have to give it and trust your partners decisions. The whole idea is to negotiate boundaries and come to an agreement about how your relationship will and is unique to the two of you. Then you follow those boundaries, try them on, change them if need be and trust that they will act with integrity and stick with what's agreed to. I don't hear any of that happening and wonder if perhaps this is why you hate this woman so much.
I would like to bet that in sorting some boundaries out, talking about feelings together, your and his and establishing some compassion/empathy between you, him and her will mean your hatred is lessoned. It might even go away. Or at least turn into compersion laced with *good for you, keep it over there please*
I get the feeling that there is some denial going on here or perhaps he isn't all that into you. He doesn't sound all that committed to you and you sound like you are in some denial about him being committed. Maybe sorting that out and seeing your relationship for exactly what the two of you are it as is in order? If you are mono, perhaps that means moving on to someone that wants to be with only you. That way you can have the commitment you need and not the stress of his other partners he thinks he can fling into his life with no work at all.
Anyone want to be friends on Facebook?
Send me your name via PM