Yeah you all need to remember that Shizuka was the one to actually cut off with Kaoru even when she was blackmailing her. She said to herself she will never go back to her. It's just that she's really confused and disillusioned.
I feel like a lot of people forget this. Shizuka tried to cut her off completely before but Kaoru practically made Shizuka believe that she'd kill herself if she's not around her. And before meeting Mask/Tokino, whenever she didn't have Shizuka's undivided attention, she'd either try to seduce her and/or hurt herself and guilt Shizuka into feeling like it's her fault.
Dont get me wrong, I like Kaoru. But that's because I like charming yet terribly manipulative characters.
I'm ultimately into Tokino x Kaoru more, but Shizuka x Tokino could be a pretty fun disaster!
I'd love to see that. It'd be hilarious. Kaoru would either be terribly depressed about it or be so into it that she'll try to make herself their third.