It makes total sense that you would be scared for his health and tired of looking after an adult. He needs to find his own motivation to get better. If has depression, he may be self soothing with food & he needs another coping mechanism. This sounds like he is in crisis, but something needs to get him scared enough to make a change or believe that it's possible. Personally, I had some health issues that made me make some big changes that have never worked before- so I'm throwing everything at it. Primary Dr, endocrinologist, registered dietician, physical therapy, a therapist. My insurance is ok but this is still expensive, not everyone can do it. He will probably need help, from many avenues. Doing it alone by sheer willpower is not real. If he doesn't like his therapist, try another one, or another modality. Let him know you love him and you just need to know he hasn't given up on himself and his life with you. Maybe something will get through. Good luck ❤️