The Diary of Carlota (2010)

17-year-old Carlota is in love with an athlete named Oriol but discovers sex with Sergio, every mother's ideal son-in-law. Carlota is in big trouble but neither her parents (who are separating) nor her best friends (Elisa and Mireia) can help her. Among other reasons, because Elisa disguises herself as a boy so she can get close to Lucas, who she is madly in love with, and because Mireia intends to seduce young Oriol, thus betraying her best friend.