You said she turned mono after a month or so...I take that to mean she stopped wanting to be with you. But it could also mean she wants to go back to just her and him.
Has anyone asked what she really wants.
It's got to suck being caught in the middle or left out in the wind. Take care of yourself in this....lets not forget she wanted to open up their relationship. And with that I feel she has a much higher burden of responsibility to deal with her negative feelings. Its a nice suggestion to back off but I don't know how far I'd take that. To me it seem unrealistic to break all contact for a period of time then get the green light and jump back in where we left off.