Monica was masturbating while watching us

As Monica got closer I noticed some peculiarities in her appearance. Her hair was disheveled, her face was flushed, her top was a mess, and most telling of all, the skirt she was wearing was hiked up. I could even see her white panties had been hastily moved to the side and not put back correctly.

"Monica," I said slowly. "Were you..." My voice trailed off. Melody gained enough sense to slide off of me and cover herself with the bedsheets, but she was still frozen in fear.

Monica's eyes suddenly darted to the side, seemingly embarrassed. She stepped even closer, and I could even see a hint of wetness on her fingertips.

Holy shit. She really was touching herself while I fucked her sister. Who knows how long she had been there too. I had no idea Monica was this perverted. Was she just into watching people have sex, or maybe she wanted to join in. Either way, she still didn't say anything, so it was up to me to make the first move.