I think Cobain just listened to too much of his own music and finally said: "A lot of this just really sucks" and KA-BLAMMO.My guess is that he awoke one morning from an drug-induced haze, saw Courtney Love and said,
"Who's that skank?"
"She's WHAT!?!"
...and promptly (and justifiably) blew his brains out.
Well, I heard that his friends told him that if he had half a brain, he'd quit doing drugs.