This dates back to one year ago. My sister in law was very attractive and I have always had a thing for her.
One day we were at her place, chilling and so on. At the time she was pregnant with her first baby.After dinner everybody fell asleep, and I noticed thar her phone was standing there all alone, so I decided to check it out to see if there were any interesting pictures which I could use for jerking off.
While I was scrolling (still had not found anything interesting btw) I was excited by the thought and the bulge in my pants was already visible. In this situation, I started teasing my cock just a bit to keep it hard, and did not notice that my sister in law was awake and staring at me.
Since I did not notice that, I just got up from the couch and started walking through the stairs in order to go to the ground floor and have more freedom to jerk off, since I was starting to get all worked up.