Dangerous Relationship with Girlfriend's Sister: Nozomi Mayu IPZ-465

My girlfriend's younger sister, "Mayu," is actively seducing me! Her cute smile and innocent eyes confuse me! We've been doing oral sex in the hallway, she suddenly barged into the bathroom for breast sex, and we're even having sex secretly in the room next to my girlfriend's! I know this relationship can't last, but I just can't control myself! What will become of this dangerous relationship with my fiancée's sister...?!