If you want to conceptualize his mental health issues as a disease that he didn't choose, that is perfectly valid, IMO. I agree that the marijuana use is secondary to his psychiatric problems. I think you need to take the analogy further.

End-stage COPD or metastatic cancer are diseases that are progressive and terminal. With excellent care, life expectancy can be prolonged and distress can be modified, but the eventual outcome is fore-ordained by the diagnosis.

Given your husband's failure to ever have achieved any emotional maturity, along with his character deficits, I believe the following: His psychiatric illness is chronic. It is progressive. And it is terminal. The long-term outcome is not in doubt.

Over time, he will continue to deteriorate. The kind of man he is now is the kind of man he will die as. There is nothing within him that recovery can be built upon. It is entirely possible that he is doing the best he is capable of. His capacities are collapsing before your eyes. He is not employable, and he never will be. He is incapable of shouldering responsibility. That is not going to change. There is no medication or therapy that fixes his basic problems.

Outside the shelter of this marriage and this home, he would likely become homeless and disintegrate faster. He very well could become in danger of harming himself. He surely would be a danger to himself, if only through grave self-neglect. If watching that, or knowing that is happening, is something you cannot abide, then you have the option of continuing to provide him with the shelter of marriage and family life. That is a defensible decision for you to make. He is your husband, and you love him. In a very childlike way, he loves you (because you are taking care of him.) I don't see where your children or you are under threat of imminent harm. Living with him is not a happy situation, but it is survivable.

About the only thing that would interrupt the progression of his deterioration is if he were incarcerated for a lengthy span of time. It would interrupt the substance use. It would impose discipline on him that he couldn't evade. I've worked in correctional facilities. Some individuals are safer and healthier locked up. My bother (who has issues with severe immaturity and poor character) was in a federal prison for several months. I wish he could have remained there permanently. He was his most well self, while there. Your husband seems to not have behavioral tendencies that get him in trouble with the law. Plus, he has been sufficiently relatable that he was able to induce a woman to stay married to him for 20 years. So he is at a higher level of integration in society than the poor souls you see sleeping under bridges. He is physically better nourished and healthier than they are. However, his trajectory - were he not sheltered - would be exactly in the same direction.

Whatever bad things happened to him earlier in life have damaged him beyond repair, especially given that he believes those unfair experiences absolve him of any obligation to be a responsible person. He does believe that. He will never relinquish that belief. Any therapy that explores how he was hurt in his early years will simply reinforce his belief that he was wronged and that how he is is all he is capable of.

Your options are to cut him loose, and he will completely fall apart . . . or . . . continue to shelter him, and he will deteriorate much more slowly and not so painfully. Those are your 2 options. Either one is defensible to choose. It is awful to have to make that choice. You want to believe that there is a 3rd option. There is not, except in your fantasies. You may need to cling to that false hope. That is your right also.