Sorry to hear that; it is a bit depressing isn't it. I have no idea how old he is, how bad his diabetes is, what his weight is etc. so difficult to give any advice. However, it is great of you to come on here as there are a lot of lovely people who will give you (and him if he will read it) masses of useful advice. The way to staying healthy, or regaining your health, is to take control of your diabetes rather than letting it take control of you. He is lucky in that you appear to be trying to help him which is great.
Sadly my husband won't alter his diet at all so we cook and eat separately; if I ate what he cooks it would kill me!!! The way to go is low carb, high fat (LCHF) as the low carbs help to keep your blood glucose under control and the high fat stops you feeling hungry. If you give us a lot more details we can all help you as well as giving support to you both.
Please get him to use this forum and take the good advice he will get along with the help his Dr/nurse gives him.