For a little context you can go back to my previous post about how my naughty relationship with my SIL started. This happened after that.

This SIL came over to spend the night again and my wife and I decided to put a movie on. We have a sectional couch and my wife usually lays on one end and I lay on the other. This was the case, so my SIL sat in between us. We all had blankets, so causally, midway through the movie, I slipped my hand under my SILs blanket, in a way that my wife couldn’t see. I began lightly touching her thigh. She was sitting with her knees up in front of her almost in like a fetal position. So I was able to work my hand between her ankles and upper/rear thigh, so that the back of my hand was resting against her pussy. She was in thin pajamas and as I gently rubbed her pussy. I could feel her pussy start to soak through her pajamas. After awhile of this my wife got up to get some water from the kitchen, so I had to move my hand back.

When my wife was out of view I looked at my SIL and winked. She smiled shyly. And I pulled my dick out of my basketball shorts and she gasped and then licked her lips. I heard my wife coming back and put it away.

After my wife went to bed, her sister and I stayed up for awhile exploring each other. She asked me to cum on her tits. I did and as I was getting a towel to wiped it off, she put on her shirt and slept covered in my cum. It was a fun night.