kanojo ga senpai ni ntr-reta node senpai no kanojo wo ntr-masu
Japanese title: 彼女が先輩にNTRれたので、先輩の彼女をNTRます
English title: My Girlfriend Cheated on Me With a Senior, so I'm Cheating on Her With His Girlfriend
Author: Mihiro Shinden
Character design: Kagawa Ichigo
Manga artist: Takarano Island