Because I Like You!!

Best friends Satsuki and Yukue are currently juniors in high school. To protect their friendship from the complications that stem from "boy problems", they made a secret promise to each other in middle school that if they developed a crush on someone, they would not tell the other. However, for some reason, to Satsuki's dismay, Yukue breaks this promise...?? (Source: Shueisha, translated)