I have no siblings, so my cousin (female, 16) is like my sister. I stay at her house a lot of times, but I was too young to see the opportunities.
Recently, one day while in my cousin's bathroom at night to brush my teeth, I noticed she left her clothes from that day all over the floor, I also noticed her used panties. I immediately closed the door and picked the panties up. I pulled out my cock and started stroking with my right hand as I held the panties to my nose and mouth with my left.
She had left some juices on her panties, but I didn't care because I was so horny by that point. I then thought of the gold mine she would have in her room. (Luckily she was sleeping in a different room) So I ran into her room and grabbed a few more panties from her drawer and took them back to the bathroom. I was so close to cumming already with her dirty panties in my mouth and her other ones around my dick.
I quickly grabbed her lotion bottle and held my dick up to the opening and shot a huge load inside, I then took her toothbrush and wiped the rest of my cum on that. The next day when I saw her using her toothbrush, I got a huge boner and repeated what I did the night before.