It sounds similar to cozy obsession, but the seme was the one who finds a book in the library. Even if it's not what you're looking for I do recommend you give it a go if you haven't already read it before
Is it one step from the end?
https://www.mangago.me/read-manga/one_step_from_the_end/
I love cozy obsession! Unfortunately it isn't tho thank you!
YES !! That's the one thank you
It's where the mc (uke) has a seemingly unrequited love with his long time friend (seme) and suddenly a book appeared seemingly detailing accurately his life and his friend pls help me find if if you know huhu ┗( T﹏T )┛