cocomocha I really hope you're feeling better today.
I agree with everything Ferdinand's been saying.
Yup, that conversation shouldn't have been happening in front of the kids.
And no, you shouldn't have hit him. But no, it was not abuse, it was weak desperation as you were desperate just to make him stop. He'd ignored, misunderstood or belittled every attempt you made to communicate with him verbally. You were feeling devastated and attacked. In the moment, it felt like the only way to make him hear you.
And, as some PPs have pointed out, it is not the same as abusive violence. It was more an instinctive attempt at self defence. Not OK, not mature or rational or a productive contribution to the conversation, but not in itself dangerous. Sounds like as an isolated incident and as such highly unlikely to escalate given that you know for yourself you shouldn't have done it.
But you really need to find time to discuss this stuff (and more) when your children are not with you.
And I think you would definitely both benefit from some relationship counselling, sounds like you both need some help (and an umpire) to communicate with each other and move on from this miserable situation.
I hope it gets easier soon. 