Was she really real?

It's about a boy named Lucan in secondary school who's convinced that he's fallen in love with a girl but does not remember how she looks like. All he remembers is her black hair and her voice. He's determined to find her. Everybody does not know what's he's talking about. No body believes him except his older cousin Artemis. A classmate of his sounds exactly like the girl he fell in love with but she claims that she doesn't know him. How does he find his mysterious lover?