It was a oneshot (well, a few chapters long), at least a 5 years old from publication (I think). It is NOT Gohoubi wa Shitsuke no Ato. A loan shark [I think he wears a colorful shirt but can't remember] comes to collect money from a guy (uke?). Uke ends up falling in love with the loan shark and not paying (even though he ends up having the money to) so he can keep meeting the loan shark. Uke ends up giving him head at one point I think.

Found another post about it, it's Hatsukoi chapter 3, by Kakine