If it is any help to you, I know of a woman whose husband was abusive — all of this happened when their marriage was crumbling — and it turns out his bizarre behaivor was due to his being bi polar. It happened out of the middle of nowhere.
She is divorced from him 17 years already — and during that time, they more or less became “buddies.” She says she gets along better with him now than they did when they were married.
Your stbxH probably has a drinking problem which is extrinsic of his Graves.
Based on the drinking, you need to tell him you won’t have any contact with him while he is under the influence and NOT clean and sober with the help of AA or a drug and alcohol counselor — and that your attorney will contact him for anything legal.
And then stick to your guns: he’s out of your life until he cleans up his act.
I suggest AlAnon for you. I don’t know if you and he have kids but if you do, AlaTeen for them.
Wishing you luck.