Here are the comments I have made concerning my assessment of the situation the OP presented:
Glennn and all who agreed with him are telling her that her BF is an out of control brute who she should run from, That's telling her that she is a liar (or even worse, delusional).
He wittingly or unwittingly demonstrated his lack of emotional self-control.
Slapping another person when not defending yourself is called assault and battery.
Physical violence is never justified unless you are protecting yourself or another from harm. You want to define emotional upset as harm.
You don't slap a woman because she betrayed your trust.
But in reality, it is the act of an emotionally immature individual. It solves nothing.
It is never appropriate to strike a woman, or anyone, in the face simply because they violated the terms of your relationship.
You cannot visit physical pain upon her for not giving you written notice of her departure from your life.
But violence serves nothing but your bruised ego.
I've clearly stated my position that hurt feelings are no excuse for striking someone in the face.
Slaps that are the result of anger are bad news.
So, unless you can explain how any of those statements can be interpreted as me telling the OP that the boyfriend is an out of control brute she should run from, then you are a liar.
She clearly said her BF was a calm, nonviolent guy
And then she told about how he slapped her face and choked her. She wanted to know if she deserved it. And that's what others and myself have answered.
You, however, wondered if you could have spared others the psychological violence that you went through by slapping the woman who cheated on you. Your position is quite clear.