Dame Koi.(2003)

Dame Koi.

"Nice guys" are boring while "manly man" just means self-centered! Ayumi is a girl who runs hot and cold, and she tends to attract no-good men around her. Hiroki Nishikaishi, a.k.a. "Megane," is a normal guy who has had a crush on Ayumi for four years. He doesn't have the courage to confess his love to Ayumi, but he secretly watches over her every time she gets hurt in love... This is a love story filled with the realistic emotions of a strong girl who gets hurt and depressed, but will keep fighting to find a happy ending for herself and her lover!

(Source: Fairbell, translated)