@jak I don't think it was so she could be with Shimao. She said she felt like she was the cause of Shimao and Hazuki's pain so she probably thought if she left Hazuki could be happy. Not saying it makes sense, but grief does things to one's brain.
@cryum But Shinonome was sparkling when she saw them together and she didn't look happy at all.
I think the sparkles may be something like the desire for a relationship. Yadogiri only sparkles whenever the other girls are mentioned because the only reason she wants to go out with Saijou is so...
Just reminding you there are options out there made specifically for people like you. It's honestly pretty pathetic to see someone getting blue balls from a slice of life shoujo manga.