Fallen question

A Fantasy story about a Angel-ish girl who has a dream in which she has a mission to protect a human boy. In that world its an angels life purpose to do what their dream was. So she tries to save him, but someone is trying to kill him, and she aciddently falls in love with him. What is the name of the book. Im sorry I forgot the story quite a bit. I read the book in 2019 but it seemed to be an old-ish book and quite popular at the time.