I think that - with all relationships - you can only go as far as the other person is willing to with you. So if you want peace and harmony but they don't, you can't force them to respond. You can only go as far as their willingness allows.
It's a mistake to think you can always win people's better nature over by forgiving and letting them have chance after chance. Sometimes you have to see it for how it is realistically and accept the other party just won't comply with simple human decency.
Having said that, I've watched my Mum forgive people time after time, and was the only child at her mothers death bed because all the others had long since gone, not accepting the parents bad behaviours. My Mum on the other had endured her Mum's awfulness out of an unconditional love that I'm not sure I could have done in the same way. It was like a blind optimism. Somehow I think it made her the stronger person but I can't quite explain why. I'd spent a lot of time over the years advising her to walk away like her siblings did, but she refused, saying "none of us are perfect".
So although I'm saying I've leaned to see people for what they ARE and not what you WANT them to be, and respond accordingly, I have to acknowledge I admire a different way of rising above it and being the bigger person.
I think actually one crucial part may be how my Mum viewed it. She was hurt by the verbal attacks but understood her Mum had mental health issues and so gave her a lot of rope. Somehow that empowered my mum rather than imprisoned her. I guess only you know the level of damage this relationship would have on you and whether it's appropriate for you to walk or not.