Sister has an abusive boyfriend
My sister has been in a relationship with an abusive guy for 5 years. He's also an alcoholic. He has been emotionally and physically abusive with her on a couple of occasions. They fight several times, involve both sides of the families, cause of lot of stress and then get back together.
There are two sides to every coin. This guy has helped our family through some rough times. He was by our side when a family member fell seriously ill. However, he has his bad days. Just 3 weeks after this family member passed away, he again verbally abused my sister over the phone for no reason because he was drunk. Then he called my mom and me and 'demanded' that we get her on the phone. I confronted him and asked him to stop bothering us and call when he was sober. Instead he came over and I ended up slapping him and my sister because they were screaming abuses at each other. I still regret what I did. A few minutes later, I sat him down and talked to him. I have done this before and it just has a temporary effect. I sometimes have the feeling that more than being drunk, he just loves the drama sometimes. And this has happened before.
He says he would not leave her no matter what. He has also threatened her that if she leaves him, she and her 'new guy' would have to look out or he would harm himself. His own parents are bothered by his behavior but they tell us he wouldn't hurt anyone. My sister is scared of him and even tells us she wouldn't marry anyone - just so that she can keep him at bay and so that he would hurt himself or others.
I stay in a different country. The episode I mentioned above happened when I was visiting recently. Though my sister and I are close, she doesn't discuss these things a lot with me but I know she's worried. I am worried for her too.
Since his family and him have supported us before, approaching the police doesn't seem like a viable option. He refuses to be without her and he wouldn't live in peace with her. My sister can be really difficult too. She gets unreasonable and is very temperamental. At times, I wonder if I should get involved at all. But I love her and I want my family to be safe.
Any suggestions? Thanks