Well, as I suspected, she would like to return to being monogamous with her husband. She doesn't want anyone else involved. In her words, she wants it to be "just her and him, before this whole misguided adventure began".
I guess we'll have to see how that all plays out...whether a friendship can be maintained or not. Either way, it was handled in a way that was pretty inconsiderate of my feelings and I've been burned. And it's also clear that while her feelings may have changed about things, it seems his feelings haven't. That's something they're going to have to settle and I've said what I can say about my side of it. Again, we'll have to see. I've been very clear about my feelings throughout this while they haven't been.
For couples who wonder why unicorns are so rare, it is because this is the sort of thing that happens the majority of the time. I've known too many people who have been burned this way. People aren't going to be quick to jump into situations where they are still disposable no matter how sincere and earnest the couple may seem.