キミノトナリ

Protagonist Kouichi and heroine Asahi were childhood friends.
Wherever they went they were together always, inseparable from each other's side, sharing in the joys of youth. As they grew older, that friendship became love.

Life began to change in junior high school, though. Her male senpai slowly took her away with charm and guile.

They thought they would be together forever, but the girl Kouichi loved became an unfaithful whore.