Losing a friend because of her fiance! Rant/Seeking Advice

So my friends and I have been close for years. We’ve also had a private messenger group chat going for a few years that we just talk to each other on and catch up with each others lives.

Well one of our friends fiancé does not like us at all. There was a time when she and the fiancé were going through relationship problems (mainly him trying to push people out of her life) and when she came to us seeking advice on our private chat he saw it (because they share a phone) and got offended over us trying to convince her we to leave him. He started a whole bunch of drama with my cousin (who is on the chat) over it, basically threatened her on a few occasions and we finally just cut him completely out of our lives, we don’t mention him in discussions anymore and had given up trying to open our friends eyes about his manipulative behaviors.

A few weeks ago in our chat, of only about 4 of us close friends, one if my friends mentioned that she had gone to see a mutual acquaintance who also happens to be this fiancés friend. This friend just recently became single. She said that she just wasn’t interested in him like that to us. I mentioned I heard some stuff about him from his ex and that sometimes he can be overdramatic.

So out of nowhere this guy she had seen told her he knows what was said about him in our group chat and that he is angry with her over it.

Our only conclusion is that our friends Fiancé once again got ahold of our group chat and is determined to make us look badly. He’s mentioned that he has read what we’ve said to each other a few times

This is so upsetting because it’s an area for us to share things with our closest confidants and sometimes we do say things we really want to keep private. We never meant to hurt the guys feelings, it wouldn’t have if what was meant to be private stayed that way.

So back to seeking advice. We’ve really been urging our friend to put her foot down with her fiancé about leaving us alone. Honestly the easiest solution would be just taking her out of the chat, however her fiancé has pushed us so far away it’s literally the only real communication we have with her, I don’t want to just say thats it with the friendship but it’s going too far. Any advice on what to do or say?