I know it's been awhile since I recommend fanfic so,
A second chance by softjungoo
Summary: " ‘The dream’, as he calls it, started about 6 months ago, and they’ve been happening every other night since then. At first, he’d just brush them off. It was normal for him to have strange dreams sometimes. This time he was quite impressed with his mind for making him a handsome prince who lived in a gorgeous kingdom. But then the dreams started to happen in patterns and they started to tell a story. The story of him and a servant boy."
Or, Jimin dreams about a boy he loved
https://archiveofourown.org/works/10974042