Stealing the Short, Stacked, and Cute Nanase-san from Her Delusional Ex-Boyfriend and Making Her Happy

One day, on his day off, Ogami Yuusuke happens to come across his classmate, Nanase Hiyori, confronting her childhood friend, Yoshihide Kouma
The two had actually been secretly dating for a year, but during that time, Yoshihide was also dating other girls, cheating on Hiyori.
After Yoshihide brazenly throws some cruel words at her, Hiyori runs off heartbroken. Unable to just leave her alone, Yuusuke follows her and decides to talk to her.
This becomes the start of their friendship, and Yuusuke gradually grows closer to Hiyori.