His way of dealing with things right now seems to be exactly what you described your personality change to be. He goes to work, gets home exhausted and shuts out everything. He sometimes mentions what he's going to do in the future, other times jokes about how he's probably dead by the time whatever's done. (in fact, he did that today and to my own surprise, I took it really harshly. He then realized that joke went overboard and apologized for it)