Itsuka Watashi wa, Kimi wo Uragiru

is a japanese manga series written by Sakurai Mizuki. It began serialisation in the September 2016 issue of Manga Time Kirara Forward.

The series was released under 3 volumes from February 2017 to April 2018.

Synopsis
"Hey teacher, why do people betray even their favorite people?" A lonely girl who pursues "why", her first love and first love (Willen Uiko). A friendly female teacher, Aiko Hitoshi, who was fascinated by the girl. By meeting two "teachers" and "students", The peaceful days are dyed with mystery and betrayal, and even ephemeral collapses ... "Why" do people betray people?, "Why" do people fall in love? A betrayal youth mystery spun by a newcomer.

(Source: Amazon JP - Translated)