Physical Abuse, unless it instantly is countered, such as he hitting you and you knocking him out or stabbing him, escalates.
The first slap he gives you will be followed by tears, apologies, promises, and the inference that you caused it. If those scams work, it will continue and escalate.
When he hits you that first time, how you react sets the stage.
If you leave and never allow him near you, which maybe 0.1% of all women do, that is the end of the Abuse.
If you accept his apologies, you have now volunteered to become a punching bag.
Physical abuse is never a one off.
It is always the culmination of emotional, intellectual, spiritual and verbal abuse.
If you don’t pack up and leave the first time he makes you cry, or the first time he tries to make you feel stupid, or the first time he spoils something for you, or the first time he insults you, you are going to get that slap.
If you don’t leave before, leave at the first slap while you can.