Oneulbuteo Cheonsaengyeonbun

Rising stars and longtime childhood friends, So Dakyung and Ji Minwoo. The scandalous open 'business relationship' is rapidly evolving to 'marriage'! But somewhere in this whole marriage, is something a little suspicious.
"Before the summer you turn 29, you must succeed in marrying So Dakyung."
What kind of story did he have with his old note?
(Source: Naver, translated)
Note: The chapter count includes 3 side stories.