L.A.
This sounds like depression. I have been through this and so have many of my friends. I never believed that "normal" people got depression and could "hold it in" so well.
Please allow your husband to try medication and therapy.
Celiac disease can be stressful and depressing. Many times when someone has a loss physically it can make you depressed thinking you cannot have certain things or do certain things. It also makes us see our physical changes as an indication of getting older.
Also he is probably at an age that depression can hit men. They start to worry more about the future and mourn the dreams he once had, that will probably never be accomplished. If he is the main money maker, this is also a very stressful time. Even my husband who has a very secure job, is in charge of making all kinds of hard decisions that effect others and their employment. That is a lot of stress.
Depression is a disease just like his Celeriac. There is a chemical imbalance in his brain. He needs professional care.
None of this is because of anyone else in his life. No one should judge or take any of this personally. These are HIS feelings. Men do not talk the way women do. They mull it over. This takes lots of energy.
I know you will be there to support him, He can work through this, but it takes a lot of energy and really just does not have it right now.