Has anyone else been there, when everyone else tells you he is a dick and to leave him to it? How do you support someone you suspect is suffering from depression and related anxiety/goodness knows what, but who keeps it secret? He obviously isn't right, and is sort of withdrawing from all his usual interests. His mother is also terribly ill, but he doesn't respond that well to anything but texts.
If you think he is clinically depressed etc then the correct support is to get him medical help. You can, for example, contact his GP, explain your concerns and ask them to pay him and his mother a house-call. If you think his mental condition means his mother is being neglected you could even alert Social Services.