Kao dake Ii Classmate ga, Yatara to Guigui Kuru Yuri no Hanashi.

Ritsu Kaido has a boyfriend, whom she is dating just because they're both members of the popular crowd. On a summer day, she and her boyfriend were about to celebrate their one-year anniversary, her classmate Tsuzuri Yarai sees them about to kiss and intervenes...? The story is about an ordinary high school girl who falls in love with another girl who is energetic, kind, outgoing, and beautiful, too. (Source: Kadokawa, translated)