To X Who Doesn't Love Me

Seo Hee-soo is studying at university and wants to become a lyricist. She has never had a boyfriend in her life, and her self-esteem is almost zero. She happens to find a magic notebook with lyrics. This notebook is able to make anyone fall in love with its owner. The thing is great, useful, but of course there is a "but" — such love lives only for one month.
Jeong Shi Ho is the main character's best friend. The guy knows about the magic notebook. And he is very worried when a girl tries to use it.