How it went, hmm. First, I should say that my husband wrote to B., his friend, and apologized for leading her on yesterday and said that he really did just want to be friends at present, which is what he'd said to her up front too. He did not mention me at all, for all she knew I had no problem with what happened between them, or possibly didn't even know.
B. still wanted to ride with us to the poly dinner, which we did. She had zero interest in getting to know me at all, either during the ride there, or at the dinner, even though she sat next to me. I was friendly and polite but she clearly had no interest in me as a person, didn't ask me anything about myself, nothing, although she seemed to have fun talking to a couple of the men and to my husband. I don't know anything more about her than I did before.
I was thinking before tonight that I might easily decide she was OK after tonight and tell my husband to go ahead and date her if he wanted to (when he's ready to date, he really isn't right now, as he has told both of us), but I am not going to push a relationship with a potential metamour who has no interest in relating to me at all. I expect my partners to be friendly to my husband too. They don't have to be his bosom pals but I would hesitate to get involved with someone who was cold to him and disinterested in him.