While the story of Beatrice and Lemony's relationship is presented as real within the world of the books, it's a fictional narrative created by Handler. There's no real-life equivalent to Lemony Snicket or Beatrice, and the events in the story are purely fictional.
However, the story of their romance and Beatrice's tragic fate serve as a powerful backdrop for the series, providing a poignant element of loss and melancholia that permeates the books.