Oh, I am sorry to hear this. There are probably several things going on here. As you hopefully know, if you have ADHD, the adderall can give you a bit more control over your life. It can reduce your impulsivity, strengthen your ability to concentrate, and many times it will help with anxiety and/or depression because it helps you overcome some of those things that had been making you anxious or depressed.
There would have really been no problem with him going cold turkey. That happens every night as the adderall leaves your system. Now if the 3 weeks had been used to develop coping skills, that would maybe have made sense. But even then, once the dose dropped, it probably wasn't working for him anyway.
I also wonder why his doctor took him off the Adderall. Taking medical marijuana has no side effects on or from Adderall. I am guessing that the reason he was taking the MJ might have more to do with it. And whatever the reason he was taking the MJ might have more to do with how he now is acting then anything else. Was the doc who took him off the MJ, a psyc or a primary physician?
The key may have been when he said, he "wants to live more fluidly". Kind of sounds like a midlife crisis type of thing to me. Long story short, what you are now hearing about may really be your "real husband." Hopefully, he will get this out of his system and return to his prior ways. But, there is so much I don't know. The only thing I can tell you with a fair degree of certainty is that if he had been taking the Adderall for over 6 years, his personality did not suddenly change because he went off of it.
If you have any questions, please feel free to ask. I hope this helps a bit. Best wishes.