Otaku-Type Delusion Girl(2006)

Abe Takahiro is an ordinary, well-adjusted, high school student, who falls in love with his bespectacled classmate Asai Rumi, thinking she's just a cute member of the art club. Alas, his love is anything but ordinary - she's actually a hardcore yaoi-loving fujoshi who is utterly convinced Takahiro and Shunsuke Chiba, the handsome class playboy and his best friend from middle school, are having a torrid affair. With comical misunderstandings, awkward half-confessions, and the revelation that class idol Matsui Yoko is an otaku enamored with Rumi as well, poor Abe has his work cut out for him if he hopes to woo the Otaku-Type Delusion girl.

(Source: Jmanga)