OK- here we are almost four months later. Best friend and wife are through counseling. His wife has completely abandoned the idea of extra-marital partners. Best friend is complying with his wife's wishes and we have ended all potential romantic interactions and agreed to nuture our friendship. She says that she supports us being friends, but her actions are much different.
Best friend and I have had very limited social contact in the last four months and when we do, she's either there with us in a group or when it is just the two of us (after her approval of us hanging out) she is texting him. When she is there, there are many possessive behaviors she does-- fawning (and fondling) on him, bragging about their sex life, controlling the conversation to be the center of attention, etc (I've excused myself when these behaviors come up). I've also been on the receiving end of some back-handed insults by her. Concerning to me is her belittling behavior to him in front of his friends and co-workers.
It breaks my heart to see a man I care about so much be treated like a pawn by her. I think her actions come from her knowledge that I am non-monogomous and at one point expressed an interest in a sexual relationship with her husband (while they were non-monogomous). I truly think she raised the non-monogomous status for herself never thinking that her husband would pursue it himself. I have very little respect for her, but am trying to maintain the friendship with him as it is quite important to me. I've told him that while I care about him deeply, I cannot be around his wife and that she and I will never be friends. It's like I can't un-ring the bell with her. Like she treats me as an active threat.
Best friend has asked me my opinion and I've kindly and lovingly let him know that I care about him and am concerned at the way he is treated, but that I fully realize that his choices are his own. I respect his commitment to his wife. He wants terribly to maintain our friendship but it is constantly under scrutiny by her.
Because of this guy, I know a capacity for love that I hadn't known before, and I am thankful for that. But the whole darned thing just effin' hurts sometimes.