Robin, you will find lots of great emotional support here. My thoughts are that the only person you can control is you - and what you deserve is to be treated respectfully. Your children are adults now, whether they act like it or not. You can take one small step at a time. As Susie said, read the article on detachment. Begin to learn about boundaries and self-care. Go to any 12 step meeting, especially Codependents Anonymous. Keep posting here, whether or not you are able to bring yourself to change anything yet. It's hard but necessary work.
All of this hurts. There are some similarities between us. I have a grandchild who was born addicted. My two older children have suffered addiction and act out against me to the point that I have no contact with one and my grandchildren and Little contact with the other.
When you are strong enough to set boundaries, they will likely up their bad behavior, but you will find strength here to keep moving forward.
Glad you joined us.