J4J was hoping you'd come back on, have been thinking about you a lot.
So sorry to hear about what your son said, but I agree with the others that it was unfortunately inevitable that the violence your DCs witnessed would impact them negatively. I also agree that you handled it completely the right way.
The last thing you want to be doing is placating your son when he threatens you, as that's simply mimicking what he's already seen in the relationship between you and your H, and it just reinforces it.
Your DC need to know unequivocally that there is no room for violence and threats in your household any longer, and just keep talking to them and encouraging them to speak about what's worrying them.
I also agree with ceslavie - if there ever was a message to you that you cannot be in a relationship with your H any longer, then your DS's behaviour should be it. If this is the impact just one (admittedly very serious) incident of DV can have, imagine what it could do to him if he were to be exposed to this over a number of years.
And whilst your H remains "arrogant" as you say, there is unfortunately no room even to think about reconciliation or a future with him, so your visit to the solicitor and the occupation order is absolutely the right thing to do.
I know this is all so very hard, but your feelings of anger/resentment/being low are all COMPLETELY NORMAL. You have had a helluva shock, but please know that we all think you are totally amazing and incredibly strong . Your children are so very lucky to have you.