New to the whole step mom game.

Hello everyone so I’m having trouble here for the first time in over 17 years ... I got married young and me and Exhusband finally called it quits anyways so I’m back in the dating game and the guy I’m dating has a son I have kids too. My son Is 12 and my daughter is 6 recently my boyfriends son has been hitting my daughter and I’m super upset 😡 because I don’t allow anyone to hit my kids but he is a kid himself and now I’m doubting the relationship because me and boyfriend are always arguing about his son hitting my daughter mind you my daughter doesn’t hit him back at all. My boyfriend who I have been with for over a year now is perfect and I don’t want to throw the relationship away because I can’t get passed this little kid putting his hands on my child. Help any step mom with kids gone through this before .......