How Can a Strict Wife Have a Younger Brother?

Looking for a Book About Marriage First and Love Later! ! ! the Male Protagonist Has Been Secretly in Love with the Female Protagonist for Ten Years

The male and female protagonists receive their certificates at the beginning. They were classmates. The male protagonist did not dare to tell the female protagonist at first that he had been secretly in love for ten years. He gave her a necklace on her birthday (which he wanted to give her many years ago). The female protagonist is a painter. The foreign male protagonist's friend told the truth.