As someone who is trying to change - see previous stuff by me if you wish - I'd say there are no guarantees. I am in a relationship where both of us have behaved badly to abusively. I can see that now, my wife cannot. Someone above said you can't forget what was done and said and I agree with that, although my wife asks me to forget what she did and does - very unpleasant speech, control through monitoring social media or bad moods if I want to do something without her. I've given up on friends and any social activities/hobbies of my own to keep the peace but then the resentment builds and I get moody and miserable so the toxicity continues.
I'd say I'd have a better chance of change if I was on my own but it's still only a small chance not a guarantee. Within a relationship that is, for want of a better word, toxic, I'd say I might be able to change who I am with others but not our relationship dynamic so real change cannot happen.
That said, I've been advised by some that we should stay together so we don't hurt anyone else bar ourselves. If I left I'd be happier and she more unhappy - is that fair?
It's never something I'd recommended to anyone else. I'd say if there's abuse leave and do the honest hard work on yourself whether you are the abuser or the abused and don't have a relationship again until the work has been thorough. And don't lie to yourself or make change conditional on others changing.
Imagine yourself tested to the limit, will you really respond differently now? Can you see what you did that was wrong or unhelpful to you and others and do you understand why you did it and why you didn't do something differently.
Do you have empathy for those you hurt, do you now really feel what you did was wrong. Have you worked hard to make amends, truly apologise without expectation of forgiveness from those you hurt.
Can you come to value the changed version of yourself (self dislike seems to be a predictor of unhelpful ways of behaving to others and self in my opinion)
If you are hoping someone else will change then ask yourself those questions about them. If you are coming up with anything but solid yeses then the odds are stacked way way against any meaningful or long lasting change.