Update on the situation:
The hostess of the gathering, whom I have only met once, listened to my concerns about former metamour respectfully. Then she went to my supposed friend and asked for more information about metamour and the situation. Friend apparently told her some version of "Don't listen to persephone, former metamour is just fine and dandy and will be a credit to your group." The hostess then got back to me and said that she did not feel she could reasonably bar someone from the group on my say-so. I don't find this unreasonable, since the hostess and I barely know each other. (She doesn't know my friend any better though.)
So, my friend knows that I raised the issue with the hostess. In addition, I know that my husband has written to friend multiple times this past week, pointing out how the situation looks to just about anyone else, and asking her to contact me to talk about it. She has not. I think husband may be having second thoughts now about us continuing to invite her to parties, etc.
I don't feel like I can do anything at this point than consider her a non-friend. This makes me sad. I used to think we were very close. I'm also sad that I can't attend the event when metamour goes, and I am sure she will go. It's just too small a physical space for me to be comfortable with a toxic and hostile person in the room.
Thanks for everyone's input here.
Last edited by persephone; 06-18-2012 at 10:06 PM.