Looking for

A webtoon/ manwha It’s one of those romance isekai types. The details I remember is ML is a blonde prince. Who is doomed to die. There’s a book and when a letter disappears from the title he’s closer to death. FL is a commoner is brunette/ black hair. I think she met the prince in a library. They’re trying to prevent his death. I am unsure if this is their first or second life.