We're Soulmates Starting From Today is a Manga/Manhwa/Manhua in english language, Comedy series, english chapters have been translated and you can read them here. You are reading chapters on www.mgeko.cc fastest updating comic site. The Summary is

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?