So today my best friend told me she's getting back with her ex. Im wondering if I handled the news bad or if I should stick to my guns. To give some background story:

They've been separated for about 5 months. Prior to that they'd been dating for 6 years. They have two small kids together. He's been verbally and mentally abusive the whole time. He manipulates everything and makes all of his problems her fault. He barely does anything for their two kids and shirks his parenting responsibilities constantly. He yells at her, swears and screams in her face for the smallest reasons. Any time she threatens to leave, he threatens to kill himself and says it's her fault. He has cheated on her at least twice. He has a gambling addiction and will blow money that is supposed to be spent on their kids groceries on gambling instead. I've have to buy their groceries a few times because of it and he makes very decent money. He hardly ever contributed financially and has been an abusive asshole for 7 years. She finally plucked up the courage to leave him and said she was doing it for her kids. She has told me COUNTLESS TIMES not to let her go back to him or stay with him because of the way that he is.

Well she's very Co dependant so that didn't last long and today she told me she's getting back together with him.

I told her that she's an adult and allowed to make her own decisions but that I want to draw an obvious line upfront and told her I don't want to hear about it when he treats her like garbage again In a week. I said I know that's harsh but I love her and I'm tired of seeing her be abused and I don't want to hear it anymore if she's choosing to get back with him.

Does that make me a horrible friend? Should it matter? I honestly can't handle it anymore. What would you do?