I think we learned two small, but important bits about Touko and Yuu. First, from Yuu’s friend Natsume, we hear that Yuu has always had pretty muted emotional responses – not crying in victory or defeat. Her not feeling swept off her feet seems like a consistent part of her temperament. Therefore, her expectations from love songs and shojo manga are never going to be met.
Second, Touko’s parents or at least her father think she is pushing herself too hard. They are not the ones pushing her to live her sister’s life. The pressure is all internal. On the other hand, it seems to me that Touko always had the ability to be what she is now. Perhaps, to be cruel, her revered older sister needed to be removed for Touko to reach her potential.
It’s hard for me to guess how Touko will react when she finds out that Yuu is in love with her Sometimes, she acts like she would welcome it, like when she was happy to see Yuu laugh and when she wanted Yuu to kiss her instead of her kissing Yuu. Other times it seems like she would freak out, like during the umbrella sharing. And then that phone call at the end of Chap 19, where what Touko wanted was Yuu’s uncaring response, contrasted with Yuu squirming on her bed in delight.
There is a lot going on in this manga, so much that I’m uncomfortable trying to predict any sort of outcome. I do feel that an end where Touko and Yuu are not together is not guaranteed to be a bad end