How to Not Get Cheated On

I'm Mami, a girl who's always played on by guys.This time I thought I was his favorite girl,but when another girl knocks on the door of the hotel room,I get thrown out into the veranda,practically naked! Although the guy next door, Iwase-san,saves me,he seems to know everything about my situation. Moreover,he takes the opportunity to give me an "ecchi lesson" so that I won't be cheated on again...! (Source: Renta)