I'm looking for a romance novel. I can't remember the title, but the general content is as follows.

I don't remember the name of the book. I hope someone who knows can help me: It's about magic. The female protagonist in the book seems to be 16 years old, but I don't know if she's 15 years old (about this age). She accidentally transmigrated to 1000 years ago and got together with the magic priest (male protagonist) at that time. The real opening of the book was when the female protagonist was in the modern world. Then, he happened to meet the priest. At that time, the female protagonist had already forgotten about the priest. In order to find the female protagonist, the priest sealed himself on a tree. He did not know if his memory was sealed by a woman who liked him in the same generation as him, or if he had stayed on the tree for too long and lost his memory fragments. The female protagonist seemed to have named the male protagonist 'Little White' in the modern era. The woman who sealed the male protagonist's memories was also in the modern era. She was also the female protagonist's classmate and good friend. It was like when the female protagonist helped the male protagonist search for his memories, a petal would appear when he recovered a part of his memory (it could be something else). When only the last part of his memory was left, the last part of his memory appeared. In the end, the memory showed that the male protagonist was looking for the female protagonist's good friend, the person who was in the same era as him. [Actually, the last memory was created by the female protagonist's good friend using magic, which means it's fake.] In the end, the male protagonist and the female protagonist's good friends disappeared. In order to help her sister, the female protagonist's brother used his eyes in exchange for the chance for her sister to go back to 1000 years ago. Then, the female protagonist went to find the male protagonist 1000 years ago. Uh, it was a book that had already been published. The content was related to magic and involved a little bit of transmigration. The female protagonist seemed to have given the male protagonist the name Xiao Bai in the modern world. The male protagonist was the High Priest of Magic from 1000 years ago. When the female protagonist was in her teens, she accidentally transmigrated to the male protagonist's era. After about a year, she returned to 1000 years in the future. In order to find the female protagonist, the male protagonist sealed himself in the tree for 1000 years. In the end, the female protagonist and the male protagonist did not get together because the male protagonist had disappeared, but the female protagonist had gone to look for the male protagonist.