I'm looking for romance manga where a lover's personality changes for better or worse. The cause can be anything from black magic to amnesia to just random will to change.

I can think of Diamond Dust (Kang Hyung-Gyu)

Brain tumour changes his playful personality into a bitter one but she sticks with him until the end.

Noting manga like that Six Half or Lover Discovery don't count because they are not actually in a serious relationship when they experience personality change.

Particularly looking for manga where the lover goes insane.

Favorite Art:
Oboreru Knife
19 Days
Gangsta

The 5th one-shot in Sheets no Sukima was the one which immediately struck me.

[img]http://i60.tinypic.com/2dj58x1.jpg[/img]