This happened to me some years ago. I had been round to one of my mates houses and he had a couple of porn books that he stole from his brothers room. He told me to take one home where I could have a good look at it.
On the way home I started thinking about all the lovely women in the book and I was getting quite horny. When I got home mum and dad were in. I really wanted to have a good look in private without being disturbed. I thought I would go in the shed. I managed to get in without anyone seeing me.
On one of the shelves I placed the book and started to look at the sexy women. Before long my cock started rising. I pulled my jeans and pants right down to the floor and started slowly masturbating. Each page I turned getting faster and closer to orgasm. After about five minutes I started cumming. I was shooting cum all over the book, it was a wonderful orgasm.
Just the second I had finished I glanced up to see the woman from next door looking right at me through the window. I froze and didn't know what to do. Quickly I pulled my jeans up and ran out. For months after I was worried she might tell my mum or dad. As time went by it was clear she wasn't going to say anything. I started thinking about it, wondering if she enjoyed seeing me pleasuring myself. It started getting me horny to the point I was masturbating thinking about making love to her.
The most exciting thing about it for me was I don't know how long she had been watching me. I still do it thinking about her now.