Should I be furious? Trigger warning *sensitive?

Anonymous
So my bro has a toxic girlfriend... emotionally coercive, moans if he goes out with mates for a night, he's even come home following arguements about him having a night out with family. She has history of drug abuse an alcohol problems. A few weeks ago she went on a 3 day binge on coke and slept with her ex boyfriend (drug dealer) that supplied her said drugs. This was during a split up from my bro. Anyway, the next day told my brother that she slept with him, they 3 says later said he raped her... told my bro she would report him, an then didn't. She has 2 kids also to her ex partner, which makes me feel even worse about the whole situation.
Anyway, my bro is back with her. He never stays at home (we split rent), some nights he stays here with her an I absolutely avoid her.
Today her son had a letter posted here.
My bro said it was for him when I questioned it, but it's clearly a sim card for her son. Who doesn't live here. My blood is boiling. I am fed up off being associated to them.
It's mostly because of her, but the fact he's gone back to her is a low blow for me.

I'm at my witts end being involved with this shit show. I absolutely dislike their relationship and wish he would just move out or dump her.
What would you do?
Should I be furious? Trigger warning *sensitive?
4 Opinion