In Order Not to Love You

Betrayed by the one she loved, she vows revenge on the day of his wedding. But that very day, she drinks poison and falls into a lake. As she lies dying, she makes one final vow:

'If I am reborn, I will never believe in love again.'

Perhaps because of that desperate vow, the magic tool Douglas appeared. If you return to the past within the book and survive until the final page, the book becomes reality. And the only condition Douglas offers is this:

Never fall in love. When she opened her eyes, she had returned to the past.

(Source: NovelDB)