I think, of the three of them Yuni is the one in the least fortunate position. Her desire to be wanted, to be needed isn't being fulfilled by Nanase, who she actually loves, but instead by Fuuko who's using that desire to manipulate her.
Fuuko also craves similar attention, but she's willing to take any emotion directed at her, even if it's Yuni's scorn. If I were to hazard a guess, she wants something tangible. Affection, rejection, something that she can actually feel whether it's through a passionate kiss or a more passionate slap. It's not something she can get from her notTwitter followers, they can throw praise and words at her but in her eyes it's probably all hollow, it doesn't carry the same weight.
Nanase, right now, is the only one I do not feel much for. She may have wanted the relationship with Yuni and been proactive in starting it, but otherwise it feels like it comes second for her. It makes her hard to sympathize with, despite the fact that we're watching her girlfriend getting manipulated into cheating on her. And I think that's going to be the real kicker when it comes to how, or even if her relationship with Yuni continues.