Well it seems to me that the way to move forward is to take away the stand off. You have told her not to come back until she wants to work on it? Well my guess would be she doesn't want to work on it and isn't into you for a triad. It sounds like it was nice and cozy for her to snuggle and have some sexy times with you, but that was it for her.
I would say she is scared to tell you this and has backed away as a result. It seems to me that you are ruining your friendship with her by being demandingand trying to control what happens.
She loves your man, not you from what I gather in what you have said.
So, if what I say is true, what will YOU do next? I would tell her to carry on with your man and wish them well, that you want a friendship back and then wait for her to trust your intensions. Give them the space they deserve and the friendship she needs from you. Show her that you are working towards that by doing nice things for them. Then go out and find your own girlfriend. Find your own stuff to do in oder to get your needs met rather than sitting at home wondering if they are having sex. Its up to you to get on with your life, they are doing fine and aren't interested in you bring involved in the way you want to be. That shouldn't be an issue, just informational. That's my thoughts anyway.