On the bright side, I talked to a mutual friend and found out that the other friend's been acting strange recently, and we both came to the tentative conclusion that he's acting out over being unable to cope with the way things have been changing, with people leaving and going off to college and whatnot. It's changed my feelings on the situation from bloodthirsty rage to pity. Not that I have any more clue how to resolve it now, but at least I'm no longer expecting a rational response from him, and the utter irrationality of it all suddenly no longer baffles me (which is really what was infuriating me: the inability to fit everything into the way the world works). He's no longer a loathsome madman, but a pathetic figure to be pitied and helped.
On the other, as I learned this my mother burst into the apartment sobbing, because she'd just heard from an old friend that another old friend whom she'd just learned had died in 2002 had killed himself (meaning, she learned two days ago that he'd died in 2002, and had been trying to contact people who knew him trying to find out what had happened, and just learned that he'd hung himself because he was going to court over something to with prescription painkillers). It's extremely painful watching someone have a breakdown, and knowing that there's nothing that can be done to solve it.