Deretai Kanojo no Ura Omote

Shinonome Hyouka and Mashima Iori used to be childhood friends, but Hyouka's attitude changed drastically some time during junior high. The sweetheart Hyouka started treating Iori coldly whenever they met. However, when another childhood friend, Ameya Hikari, starts to make moves on Iori, Hyouka's attitude towards Iori also begins to waver...

(Source: GC Novels, translated)