Manic depression (or whatever PC term it goes by nowadays) makes sense because of all the realism. This Joker's mental state is alot easier to speculate at then most others. Even Croc's goon could tell. But the problem with that is he's the Joker, not a garden variety manic depressive.
Obv. Batsy is his one true love, Harley knew it, there's a whole subplot going on about their complex love triangle, why else wouldn't she hug him? All the pills? He was trying to OD coz he just needs some BATSEH LURVE.
(Oh Gawd, someone brought up Hush Returns and there was some keyboard smashing. ASASDAsffAGf. OK. Breathing now.)