It's an yaoi manga about a school teacher and a student. The student is a rich kid who came from America and has some connection to the Japanese Mafia and . At some point in the story a butler of sorts comes around and the boy says the butler was his "first". The boy's father then tries to seduce the teacher in order to convince the boy to leave him (the teacher), because the boy is required to marry someone, as part of an understanding I think.

What I still remember is that the boy is very arrogant and doesn't give a shit about anyone's opinion (only the teacher's).

Thank for the help

Furimuku Dake de Anata Tsumi na Otoko, 2nd story/Chapter 3?