Welcome to the SR family!
I am so sorry about the situation that brought you here, (((cyberhugs)))
You have found a wonderful resource of information and support. Please make yourself at home by reading and posting as much as needed.
I do not have answers as to why your partner of 18 years wants to end the relationship. It doesnt not seem like a healthy decision to be making this early in his recovery.......
For yourself, I am glad you have a counselor. Have you considered Alanon meetings for face-to-face support? They really helped me feel accepted, calm, and helped me learn steps to better caring of ME.
I also recommend getting a free consultation with a lawyer in your community. I needed two free consultations (with different lawyers) to get the answers I needed concerning my rights as wife and mother in our community. I felt better about my future when I knew what my options were.