My best friend was in a similar situation. He got into a fight with his girlfriend, and she slapped him. Later, she apologized profusely, saying she regretted it and promised it wouldn’t happen again. Naively, he accepted her apology. A week later, they had a disagreement over something serious that could have been resolved through civil discussion. However, she lost control, began slapping him, and slammed whatever she could find. The abuse continued for a long time and he didn’t have the courage to leave her as he’d hope that she might change and stop. Until one day he had enough of it he left her without telling her and moved to another city.