Read manga: Kami-sama ga Uso o Tsuku.

manga
Summary:

It's the summer when Natsuru is 11. The girls in his class have been constantly ignoring him since he's turned one of them down on Valentine's Day. This changes just before summer break, when Suzumura, the tallest girl in his grade, suddenly talks to him. Natsuru meets Suzumura again outside if school and finds out she has a secret.