Yes, it was! However, my own experience has taught one thing, once it's happened, once it will likely happen again. I say this has I've seen this happen with my work with woman
Just because your husband hasn't been physically abusive before, it doesn't mean it can't happen again. You need to look at your own boundaries on this. Meaning if it happened again, would you then leave?
Your son has a hold over you all now. He can use this in blackmail, telling you he will do xyz if you don't comply with xyz.
You may need to think about discussing this with a teacher or the like. If you believe the teacher, for example, would go to SS and you're worried about what will happen, then you need to think on.
It may be that you need to take the power back from your son as he might start threatening to tell.
If you're planning to stay, you need to seriously evaluate how you take the power back from your son. He will use this over you if he is as bad as you say.