AITA for not letting my boyfriend hit me when he is angry?

My (23F) boyfriend (25M) is kind of a weirdo in a good way. He is not a chronic anger issues sufferer but whenever he is upset or irritated, he gets this weird urge to hit me (23F) because it calms him down. I have been dating him for two years and he has only done this once in our relationship and it was a weird experience for me. He hit my stomach but it was not that hard but it was still a little uncomfortable for me. But I have learned to live with it as he only does this when he is really angry. But for the last two months, I have been suffering from this sharp pain in my abdomen region. Sometimes it troubles me a lot but I have learned to live with it. I thought it was nothing but when I went to my gynaecologist she said I have a cyst in my abdomen. I am scheduled to undergo surgery to remove the cyst. I told my boyfriend about it and he apologised a lot and he promised me he would not do it again. I also told him that if I catch him hitting me anywhere then I will call it quits. He agreed to it. But he also told me that he will try his best to not hit me but if he does it in anger he will not be held accountable for it. I am not sure what to do because I do not want to end the relationship but at the same time I do not want my boyfriend to hit me. <br><br>I told my sister (30f) about it and she said I am an asshole because I let him hit me in the first place. AITA?<br><br>Edit:- I want to clear a few things. I have been in the relationship for two years and he has only done this once. I do not know how he got the idea of hitting me. But he does have daddy issues. My bad for not clarifying these before. And for the people who are telling me to leave him because he did this to you. Just remember every person can change.