Ao Haru Ride

At the end of the first year of high school, Yoshioka Futaba meets Tanaka Kou, who was her first love. In their middle school days, they attended the same school, but he suddenly transferred to another school. Three years later, he appears in front of her again with a different last name, Mabuchi Kou. His personality also seems to have changed from warm to cold. He is like a totally different person from three years ago. Yoshioka Futaba slowly learns what happened to Mabuchi Kou for the past three years, and she become to have feelings for him again.
(Source: AsianWiki)
~~ Adapted from the manga "Ao Haru Ride" (アオハライド) by Sakisaka Io (咲坂伊緒).