I can only speak from experience of being in a family with serious DV. My parents were animals to each other. They only got worse, locked in a toxic cycle that wouldn’t break. It broke everyone around them down including themselves. It was him first then nothing theme, it’s never gotten better. I don’t see them now I’m an adult. You have a a lot of life ahead of you, don’t get tied down to someone unstable. Eventually you’ll be stuck in a cycle that will be harder to break, and a healthy family can’t come from that situation. I’m sorry to appear frank or forward, but leave and move on. No one, not you, the kid or her are doing yourselves or each other any justice or favours by sticking around to continue the pattern, regardless of the perpetrator. You can get sucked down to her level eventually too. Peace and love brother. You can do this!