Kimi no Kami ga Kininarun da

Just after quitting the baseball club, Suzuhara is suddenly dumped by his girlfriend—and the whole thing is witnessed by Miyashita, who sits next to him in class. In the summer of their third year of high school, with graduation drawing near, Suzuhara starts growing out his hair. He soon finds himself strangely drawn to Miyashita, who changes her hairstyle everyday.

(Source: Kodansha, translated)