I do care! Trust your instincts and know that even Charles Manson had a mother! Not saying that your (or any of our) difficult child is Charles Manson. But saying that you have experienced a tangible event of violence. IT IS REAL.
I hope you and your husband do discuss a safety plan. That event was domestic violence from your difficult child. Look at the physical layout of your house. See possible dangers. Hide possible weapons (this includes butcher knives, etc). by the way, I'm not telling you anything that we didn't do in our own home before our difficult child was booted out (by us, at age 16). At the least, you'll be safer and sleep better at night. At the most you may save a life -- yours, husband's, or your difficult child's. We got ideas for our safety plan from an on-line site for domestic violence. It was years ago, but I have no doubt there are many remaining.
He's 18 now. Remember, you have maaaany more legal rights now. Things have shifted in your favor. I once called a domestic violence hotline and they were AWESOME with specific suggestions.
I hope this all just fades into the past for you. However, unless we take very different actions, history will tend to repeat itself. Your concerns are real and valid.
Stay safe!