I love grey heroes too, wish there were more of them both in dramas and movies.
Sigh, you've probably watched everything I'm about to mention, but I'll write it anyway just in case.
Not all of them fit perfectly, but all certainly have aspects of what you're looking for.
Cheese in the Trap - definitely not normal, has very villainous tendencies and is obsessive.
Empress Ki- unhinged and obsessive
Bridal Mask - both male leads are evil at one point or the other (poor female lead lol) and the second lead is also obsessive
My Heart Twinkle Twinkle - more evil than good and extremely romantically obsessive.
Moon Lovers: Scarlet Heart Ryeo- Very good quality drama, but I didn't finish it for personal preferences reason , but I think it fits.
