For us, the change from what seemed healthy and happy to sheer batshit crazy was slow and insidious.
While I acknowledge and agree that it would be dysfunctional for the husband to to break up with Mark for Jade, because it is he that has caused the break up, he has some responsibility - and in this case especially, because the guy in question is his brother. They all live together.
Too often it does seem to go slow and insidious-I concur.
On the next piece, I would say she has an option that isn't dysfuntional (all abitrary for the thread-but maybe purposeful to mention for someone who comes in to read).
She can tell husband he needs to deal with his brother regarding his break in the agreement and moving out AND tell him she isn't agreeing to break HER agreement.
One of the hardest, but best moves I made with Maca was when I told him that while I respected HIS right to be a dick. I wasn't going to participate. I refused to break up with GG at his request. I pointed out to him, he could take that as not choosing him OR he could realize that was the SAME response I would give GG if he reqeusted I leave Maca. No.
I don't give up friends at the request of other friends (or partners) and I won't give up partners at the request of other friends (or partners). Because my relationship with any one person is mine.
I also pointed out to Maca that when we were FIRST dating, someone I love dearly tried to play that card with him.
When someone gives me a "me or them" ultimatum, they automatically lose. BECAUSE regardless of their position or role in my life;
they clearly don't respect ME as the person I am or they never would have made that ultimatum.
OBVIOUSLY-with Maca (and it's true of all people who have considered giving that ultimatum to me); I will tell them, "this is an ultimatum I don't accept. My rule is, whoever presses it, loses. So I hope you will back down and choose another direction."
In Maca's case, he remembered, my dear friend didn't back down and I walked away from that friendship. It hurt. It hurt A LOT. But I don't regret it. She was wrong. Maca took that warning and chose a different path. I am fairly confident that he hasn't regreted it. I know I haven't.
I wouldn't have been a "bitch" to the OP's husband. I wouldn't have gotten snotty or nasty with him. But, I would have told him that I wasn't willing to deal with these types of ultimatums. Give him time to calm down and set a date to rediscuss.
But I sure as hell wouldn't have agreed to breaking up with my boyfriend at his request. That doesn't mean it wouldn't have come to a break up. They are brothers. That would be a damn near impossible nightmare.
But-I would have stood my ground and let him know that the havoc wrecked was going to have to be done by him.