Occasionally I baby-sit for my older half-brother and his wife. I have had a crush on her ever since I can remember and now I am 18 they let me baby-sit their little boy and girl. Last time I was there I washed them and put them to bed. About to hours later I went upstairs to check on them and I heard a noise coming from my brother's room.
I looked in and he had left his computer on, so I switched the volume off. As I turned around I noticed my sister-in-law's underwear lying in a drawer, so I picked up a pair and sniffed them, while my other hand went down to my cock. I started to caress myself, although I was aware of the children, but I knew they were fast asleep.
I sat on the bed and beat off over my sister-in-law's underwear. When I came I had the most terrific orgasm ever, next to the last time I spent with a girl. After, I put her belongings away and went to clean myself up. I felt really guilty and still do, but I will hopefully have more chances to go through her drawer again.