Refuses to give up cannabis and try proper meds

Thank you for all previous support. We did manage to get to a specialist psychiatrist in UK, and he told HB very clearly that he MUST give up cannabis for at least four months to clear it out of his system, before he would do a meds trial to eliminate doubt about potential ADHD. My mother in law originally read Melissa Orlov's article in the NYT three years ago, and it so clearly seemed to describe the endless mysterious issues with our marriage that caused such confusion and insecurity, and lumbered me with every single possible responsibility while he did exactly what he liked (don't know what to this day, but it certainly didn't make him happy - probably cannabis even when he said he had given up). To begin with, ie just after the appointment, he appeared to be agreeing that this was a good idea. Now he point blank refuses saying it would be like replacing cannabis with 'cocaine' and that is 'clearly a bad idea'. I think this is also because I would then be 'right' and he cannot bear the idea - that he and not me (or in fact his uncontrolled condition) is to blame for the break down in our marriage. I am sure this is not in any way a proper decision based on rational grounds and the need to restore his relationships with his wife and children. I am sure it is knee jerk reaction to his hostility and anger towards me for always trying to help, sometimes in ways that simply did not and could not work, and just caused me further pain. He did state quite clearly during the appointment that he had no intention of keeping his promises towards me. His family as far as I can tell prefer him in the state he is in - one of them 'employs' him for menial tasks and pocket money. I want the man I could see there back. If not for me - possibly too much damage - but for our three children. I am terribly nervous now, and when with him feel panicky due to all the endless shocks big and small that his behaviour caused when we still lived together. Any advice?