From Leaping into Puddles:

Bouyant girl Aizawa Yume falls for the cool boy in her class, Kashiwagi Kou—who tickles people’s noses with a sweet scent and only smiles from time to time. Slowly, Yume develops feelings for Kou-kun... but one day after school, she catches him with Hitohana-san, the girl with a bad personality and equally bad reputation!

From Chibi Manga:
Aizawa Yume, 16 years old, is a healthy girl. She got the seat next to the cool and I-don't-care-about-the-other Kou-kun !! Little by little, she discovers his true face and becomes attracted to him...

Your heart will beat a lot with this story about a sweet and bitter unrequited love !!