Break up immediately.
Any violence by any human being to another is totally, 100% unacceptable.
I'm going to give you all the reasons why you're going to break up with this girl:
- It shows an extreme lack of self-control, something that can not survive a stable relationship
- Next time she could use a weapon
- If you're hit again, you could attack back
- If you attack back, you will go to jail, as domestic violence cases are weighted heavily against men and violence against men is not taken seriously by the police or courts
- You should never suffer the insult to your integrity as a person to allow yourself such an act
- You're missing out on being in a stable relationship, free from violence or the fear of violence
For all the reasons above, you are dumping her on the curb, right now.
As in, literally, right now.