Writing a toxic pairing without coming off sympathetic to abusers
So as the title implies the issue im currently facing is the aim is to show that both characters are messed up, but im worried it reads as making excuses for the abuser. A little context before the scene in question. Both characters are from very broken homes and unstable backgrounds. They had been dating for nearly a year at this point and the arguments and fights between them have slowly been ramping up throughout the story. Finally the male MC reached a breaking point when the female MC verbally struck a known sore spot and he backhand her in the mouth. The fight ends abruptly at that point as the slap came as an absolute shock to the both of them and he immediately leaves without a word.
The scene in question takes place a few days after. Since the slap the male MC hasn't shown up to normal spots and refuses to answer his phone to any call or text from the female MC. Fearful the relationship might end the female MC finds him in his garage and another argument insues.
The male MC wants to end everything, claiming he crossed a line that you can't come back from. He claims he seen it more then enough times with the men his mother dated and that even if this time its just a slap that its simply going to be a string of promises that it won't happen again until it does. Then the cycle will repeat over and over with the gap between shrinking until its a daily occurrence.
The female MC retorts that he's not the first man to hit her, but he's the first that stood up for her. The intention is to show she has normalized abuse since she has dealt with it her entire life and that she'd rather continue being with him for the protection he provides then leave because he hits her. Her entire argument essentially revolving around the fact that abuse is a common occurrence and she'd rather be with someone that "just needs to work on his anger"
This is where I run into the problem though because I feel as if it portrays the idea that abuse is ok. I'm not sure how you tote that line properly though as thats essentially the exact argument of the other character. Like the scene is supposed to show how damaged they both are as he is terrified of become the very kind of man he swore he wouldn't be and the only outcome to prevent it he can come up with is that they simply can't be together. She is afraid to lose him as, in her view, he's the only man to respect her and care for her.
TLDR: How do you properly write a victim down playing and dismissing abusive behavior without coming across as if you the author condone such behavior.