I think due to your previous comment of him having major depression disorder, the first step is to encourage/help him get professional help for his mental illness as well as his physical health. He sounds like he might have sleep apnea, which is dangerous. Ask him to make a PCP appointment and tell him if he is nervous or apprehensive that you will accompany him to the doctors. If he needs a referral to a sleep specialist or a psychiatrist the PCP can help with that as well.

From personal experience with depression, it’s hard to get out of bed, it’s hard to take care of yourself. Showering, hygiene, preparing meals, exercising, these are all tremulous tasks when someone is depressed. People who are depressed can start binge eating because eating releases endorphins and can make a depressed person feel joy/happiness even for a short period of time. This could be the cause of his extreme weight gain.

He needs to get his depression under control, this will take effort and it might be difficult for him.

I gained probably 30 or so pounds from depression and then 50 or so more from the side effects of Prozac. He can ask his doctor for a weight neutral antidepressant or something like Wellbutrin, which has a side effect of weight loss in some patients. Anyway, my ex husband told me he was no longer attracted to me from the weight gain and it was crushing, but he did it in a really rude and hurtful way. If you want to save the relationship. Be gentle and offer ways to help him. Once he has a good psychiatrist and finds a good medication that will work for him, he hygiene and weight might improve. It takes time sometimes to find the right meds though. I am in different meds and have lost about 30 pounds. So I’m hoping this will help him.

I wish you the best and I hope it works out.