I was staying at my girlfriends house for the day and I wasn't feeling good so while she and her family went out to go shopping I stayed back and took a nap on the couch. I woke up a little after they left and I was so horny. I knew they weren't going to be back for at least two hours so I needed to find some release.
I went into the bathroom to relieve myself and I found a pair of my girlfriends younger sister's panties. I couldn't resist so I took her panties and wrapped them around my already hard cock. I started jerking off with them and in no time I was ready to blow my load. I wanted to stop right before I came so I wouldn't make a mess in her panties but I couldn't hold back and came all over the crotch of her underwear.
I continued rubbing my cock into her panties after I came and then tucked myself back into my pants. I then took the panties down to where they keep all the laundry and threw them in the pile hoping it would dry before anyone would notice, but secretly I hoped she would find it and masturbate to me cumming in her little panties.