And what would Yuu get out of it? Attention and validity, I think.
I've never sat down and really considered what Yuu gets out of all of this, but, here's an idea that has popped into my head:
Yuu has felt so disconnected from everything because no one has really shown her the depth of their feelings. Yuu can't really be with someone who is shy about affection. She actually needs someone to be as obsessed and demanding as Touko. She's observant and she pays attention to details, but her emotional IQ is completely out the door. Trying to have an emotional affair with Yuu is like trying to teach calculus to the special ed kids. She can understand that someone is in love with her, but she can't understand what that means to her, not unless it is consistently flashed in her face with big bold bright red letters everyday, forcing her to think and dwell on it.
And I don't think just any ol' person would do. If Natsuki were to have tried that, for example, I don't think it would have had to same effect. But I'm bias. I'm a firm believer that Yuu really truly loves Touko because she's Touko.