My apartment ended up with my drunk sister-in-law and her female friend after missing the last train, and they decided to sleep in a sandwich formation. Because we were sleeping in a sandwich formation, my sister-in-law's friend's clothes were exposed, and I could see her breasts and panties freely! ...I couldn't hold back any longer and touched her, causing me to get an erection. I thought I would be noticed and scolded, but surprisingly, she welcomed my erection, and we started having sex next to my sister-in-law. Moreover, my sister-in-law also noticed this and became aroused, starting to masturbate, but couldn't hold back and joined in! We ended up having a threesome!!
