Your story looks more and more difficult as you add more detail.
So he was emotionally abusing you before he assaulted you. For an hour. Does he do that a lot btw, the emotional abuse? You said he was normally loving, but it sounds like emotional abuse isn't that unusual, since you glossed over that initially.
Then you slapped him in retaliation. (That is an assault)
Then he punched you, knocking you unconscious, in front of your children. (Another assault, this time a serious one that could have ended in death)
Then he denied it, and denied you were hurt, and pretended to your terrified children that there was nothing wrong.
Your children tried to physically defend you, and he presumably restrained them/was rough with them/shouted at them. (Probably another assault)
You tried to leave after the assault, and there was another altercation, and your H violently took your son from you, roughly enough to damage his clothing (another assault)
You are now trying to find a way to make all of this "ok" so you can stay with your H, and continue, as long as he doesn't physically hit you again.
It sounds like your home is a dangerous and frightening place for your children, where boundaries are blurred and they can't predict what will happen next.
You said this was "first-time" but it sounds like there is an atmosphere of violence in the house.
Have you ever been in therapy or counselling for the emotional abuse you get from your H? Or for anything else, for that matter? It sounds like you really need support. You children must feel safe. They cannot carry on like this.
In answer to your question, where does the slap leave you -- you should not have slapped him, he should not have hit you. One of you should have walked away a long long long time before it even descended into emotional abuse, let alone physical assaults.
However his assault is still illegal, and much much MUCH more dangerous than a slap. He could easily have killed you. He has no excuse. That you slapped him first doesn't make his assault morally acceptable.
You owe it to your children to separate if you cannot resolve your problems without resulting to psychological and/or physical violence. Again, this is not about you. Your feelings for your H need to be put on the back burner -- you children have a right to safety.