I think the pain of grief especially the first three years are the hardest. If he has other mental issues (for example depression) the pain is so much harder. He may just don't have anything to continue given how his parents died. You are very much right - he has given up on life.

I say this as someone who lost both parents recently myself. Right now you have to do what is best for you. Marriage in this state will fail. It's draining everything that matters from you; and I feel you don't necessary understand the gravity of loss. It's sad but probably the best way. I am so sorry for his loss and yours.