I really feel for you, you have done all the right things and it sounds as if you're losing the battle.
To most people reading this thread I'm sure it sounds like it's time for you to pull back and take care of yourself. Does she still want to be polyamorous or is she just using you until she can get this guy to leave his wife? Was it ever polyamory? Because of his cheating, by definition, not really.
I have been through NRE when I was married and so I know what it feels like. At the time I didn't know what it was. I thought I had felt so unloved for so long that it was my own unique reaction to feeling it again and coming alive. I had all these justifications for what I was doing. Just Like RP I was in lala land and I saw most attempts on my husband's part to reign me in as him trying to keep me a prisoner.
Because in polyamorous relationships we don't have quite the same boundaries are our relationships more at risk from NRE? In the light of a few of the threads at the moment this is starting to worry me. If it happens to me again or my partner I'd like to know in advance how to handle it effectively, or even better, stop it from happening in the first place. If others feel the same way we should start another thread. so as a not to Daze and Confuse any further.
Sorry D and C didn't mean to hijack your thread. She's obviously right into this guy but for you to have any chance you need to establish if she is willing to work at at least being honest and loving in her dealings with you. If not I'd be packing my bags or even better packing hers.