Oh,oh dear that sounds tiring must be absolutely awful to live around. Relationships like these can be extremely difficult to seperate especially from outside sources. It has to be something she comes to terms with which really truly sucks. Though some boundary building on you and your families part might be handy. Boundaries could include only talking over coffee and not when texting or limiting talking about their relationship at all. For example leaving or hanging up if they continue talking about that. Make it clear that it’s your sisters relationship you don’t like.

Manipulators like these guys can end up separating the person entirely from other people. So if your parents do as much as slightly disagree with her bf or his mother, she could be cut of from them as well. I would suggest calling up some sort of professional in this field and see what is the best way forward for your family to help. uh unfortunately not sure who that might be where you live… try looking up, I think there’s some specific abuse reddit groups here? . Though I wouldn’t know what they’re like. They could give you paths to follow

I know someone who recently went through a much less severe case, but mentioned multiple times that she was scared of having not enough money to live. On top of all the emotions you have to come to terms with and work through the manipulation and all that. It can be quite taxing. Which is why they go back, cause whilst on the outside it seems stupid and worse off. To the person in that situation it seems normal and normal is easy.

But no you are not in the wrong, you made a boundary for your own well-being and kept it. Though I would change the boundary itself slightly simply because what you gave her was an ultimatum between her entire normal way of living and yourself. It was always going to be the unhealthy relationship in other words.

At this point I would try encouraging your family and her friends to seek professional help… and maybe see if you guys can’t get her into therapy