I do believe the abuser can sometimes live inside an abuse victim. We perpetuate things they said/did in our minds, sometimes even recreating events. I personally hear my aunt's voice, the mantra of "You're fat, you're ugly, you're stupid, you're, lazy, and NO one will ever love you!" I tell myself all those things, as she did. I have self-harmed to punish mistakes as she used to physically abuse when I made a mistake..
Getting to the root of why it's repeating, what helped to ingrain the behavior (even if it triggers, but if it does, do this with a good T), really plotting out the before, during, and after effects can really help to gradually replace the words, thoughts, feelings, or actions.
In cognitive processing therapy, the Challenging Beliefs Worksheet, it asks for a situation, the stuck point associated with it, emotions created by the stuck point/situation, a whole bunch of questions about thinking patterns, evidence for or against the stuck point, and something to replace it with.
I have to ask myself those questions, write them out, and try to replace that thought. Even working on 5 a week is exhausting, but so very worth it.
We can break free of that inner abuser. I'm very gradually making progress, and it feels like chains falling away. Good luck to you.