Maybe this but i doubt
https://www.mangago.zone/read-manga/dangerous_vices_of_a_gentleman_loan_shark/
But do feel free to look through the tag (theres not many pages so it should be easy to find)
https://www.mangago.zone/tag/loan+shark/
I know your searching for a mega but that really sounds like the kdrama “you make me dance” from the description of your story I think you would really enjoy it although it’s short
https://www.mangago.zone/read-manga/projection/
Could it be this?
I need to find a yaoi manga or mangwah about a loan shark who kinda likes and help his cute client…. I don’t know more because i read only first chapters, I thought it was limited run but it wasn’t… any ideas?? PLEASE