ERDM-100 "It's the very edge! Will it be found out or not?!" Reverse NTR with her best friend, reason collapses! Ahegao endurance sex! 4 hours

My girlfriend brought her best friend over, so I pretended to be a good boyfriend, but she turned out to be my type! After the three of us played together for a while, she fell asleep, and the two of us were in a good mood. I didn't want to get angry with her, and I didn't want to cause any trouble... I was agonizing over this, when the girl said, "I'll do it if you keep it a secret." What!? Is that okay? I did something naughty next to my sleeping girlfriend, trying not to make any noise...