Hi, Perfect. Welcome to SR. Glad you found us.
You must do what you must do. Mom is an addict, and will use everyone in the fam to get what she needs. Cutting ties at this time may be the best and only answer.
From your post, it seems that your husband is troubled by your attitude toward mom without understanding why. Maybe he is uncomfortable with what he sees as coldness toward mom, but that you see as necessary to protect your family.
I'm not sure how much explaining and giving the backstory will help.
Brings up a lot of past hurts for you.
I agree with another poster that simple is best. Just say this solution is best for you at this time, but that you have hope that if mom finds recovery, things could be different.
Peace.