I am so sorry. I certainly understand your situation.

Wow. This is an extremely difficult situation you are in. I can pray for you.

Yes, there are many similarities between our sons. And between us.
But I want to talk about you...I am in the same shoes and seeing a therapist to learn coping skills to help deal and cope with him, his life and decisions he is making. He is in the mid-west and I am on the east coast. But he does visit and we talk on the phone. Sometimes so draining for me with anxiety I develop a migraine after hanging up the phone. If your therapist is not helping you to see a clearer and better way for you to handle him, look for a new therapist. Mine is compassionate and has lots of good insight into my situation. Also I am now looking into family support groups for those with substance abuse, I feel my son is abusing his ADD medication (which I don't believe he has) Adderall. He did in his last semester of college. His anxiety was high as he was coming home with no job lined up and divorcing parents. He's my only child. He told me he was diagnosed with ADD by a psychologist while in college. This a high achiever from grade school up to his MBA. I didn't buy it and still don't. Obviously he never told his psychiatrist of his abuse of this drug and manipulated him to order it for him again...fast forward 20 years. I blame most of his behaviors on this drug. It clearly affects the brain chemistry in a very bad way, Highly addictive & at times he presents with manic behaviors...grandiose plans but the next day, he does nothing (he is not diagnosed with bipolar). No motivation BUT this drug is suppose to do exactly that??!! But he won't stop it. So I must help myself., he likes the feeling it gives him too much. Have you tried contacting NAMI? A great supportive group for families affected by loved one with serious mental health issues.
Do you have trusted close friends or even one friend for you to confide in? Or affiliated with a faith based organization? Both can help you. Any family you can lean on for support?
Do you need an anxiety medication or an anti-depressant to help you? Do you do self-care activities? Meditation, yoga, walking, good nutrition, massage therapy for relaxation, nature, music, hobbies to help distract you, readings on adult children with mental illness (there are tons of them), spiritual readings or even volunteering in a cause that means something to you...just some suggestions. We are both in the so-called golden retirement years. It is SO unfair we now have this to face with our adult sons. We can set boundaries, we don't have to accept abusive behaviors and we CAN put our needs first instead of letting these "men" drain the life out of us - at this stage of our lives. We deserve a peaceful and fulfilling life!
You must take care of yourself!! I more than get it, I more than understand how you feel. I am in your shoes too. And some days I am A-OK with it all. Putting my "burden" into God's hands and letting go. But some days I feel so so heartbroken with it all. This is all normal. We are only human after all. Not Super Moms!! We did the very best we could raising our sons.
As much as we wish, we can not control them. Not anymore...they themselves can only help themselves. Of course, as Moms we can plant seeds. But they can only nurture them IF they choose to. Your physical, mental and spiritual health is your priority now. I am with you on this...and we are not alone. Lots of Moms are facing such heart-breaking situations with their adult children. We can talk the talk, but only our boys can walk the walk.
The very very best to you! Take Care of Yourself! What will be, will be.
Accepting what we DON'T want in life is so very hard but it CAN be done.