You've really helped me a lot with clarity on this.
We had an open, honest, conversation on the subject. I basically told her I hate the idea of this relationship with every fiber of my being, I am losing respect for her seeing how she acts, I will never be OK with it (which is NOT to say I am not OK with poly in general), and I want and think she should end it.
She's not ending it.
I told her I don't know who she is anymore. I feel that she has been hijacked by NRE and there is "no one home". She is (or I believed was? for 8 years!) a kind soul, someone who would never hurt a fly, an honorable person.
I've made my mind clear. Short of giving her an ultimatum (e.g. quit this or leave the house) I don't feel there is much more I can do now. And an ultimatum is really not my style. It feels very violent to me as a relationship strategy.
So for now I am keeping my distance for a while and waiting for my wife to reappear.