You are not the NTA, not even a little.
You owe your sister your loyalty, and since her ex treated her badly, you don’t have to keep hanging out with him and his new partners all the time. It’s very rude of your BIL to even ask, especially since he hurt your sister and the time frame is so short.
It’s also completely understandable that you don’t want to be in a strange “let’s all stay one big happy family” situation after being betrayed like that. It’s okay to set limits. Protecting your sister’s comfort (and your own) isn’t “immature,” it’s polite and smart. It’s up to your husband whether or not he wants to keep a surface friendship with him, but you don’t have to hang out with your sister’s ex or his new girlfriend.
AITA for not welcoming my brother-in-law’s new GF into my life?
