Geo,
I am sorry for your friend's misfortunes. It sounds like he is taking a sure-fire approach to beat back the blues, however. One thing that might concentrate the benefits of cooking for this purpose is to share the shopping, cooking - or just the eating - with a good friend. Works like a charm.
I second the recommendations for
A Girl and Her Pig and the
Zuni Cafe Cookbook by Judy Rodgers. From the current cannon, I'll add David Chang's
Momofuku, already a topic on this board. All of these books recommend themselves by including dishes that could be described as comfort food, but which offer important lessons in technique.
I have another suggestion that might serve if your friend has a robust sense of humor and is not yet at the point of having a great deal of energy for a new enterprise. It is the truly hilarious, illustrated, "Eating in Bed Cookbook" (1962) by Barbara Ninde Byfield. The author is/was quite the wit. And the focus on luxuriously comforting recipes for all the woes that plague us is just the thing to cheer one up, even if one only reads the recipes.
This blog post catches the spirit of the book, which I cannot recommend highly enough. And don't take my word for it. The book made the Saveur 100 a few years back.
Man : I can't understand how a poet like you can eat that stuff.
T. S. Eliot: Ah, but you're not a poet.