In a way, this song is very much like the novelty hit, "They're Coming to Take Me Away Ha Ha." That is, in both songs, a man has lost his mind and gone totally crazy due to breaking up with the girl he loved.
In this case, following the split with his girlfriend, the narrator has become a recluse who never leaves his home. His old girlfriend has heard strange rumors about his behavior, and comes to visit him (he ascribes her concerns to a guilty conscience... and that's probably correct).
He displays all sorts of crazy behaviors, but insists he's doing just fine and having a swell time all by himself. But of course, the more he insists everything is fine, the more obvious it becomes that he's completely lost his marbles, due to heartbreak.
