This was at the age of fifteen.
I was sleeping over at my girlfriend's house, which I started doing a lot that summer. I stayed in the guest room next to her room. The bathroom was out in the hall. Her mom and dad's room was across from the bathroom.
Her mom was away, staying with her aunt that weekend. The first night there I couldn't sleep and got up to use the bathroom. As I went in I saw her dad's door open about four inches. I went in and peed. I was quite horny anyway, and as I came out I saw her dad laying on his bed naked. I walked to my room, then snuck back to his door. As I got there I could see in the low light of the TV that he was stroking his cock.
I started trembling. I had stroked my boyfriend through his pants a couple of times, but that was it. Her dad's cock was very large, and he had some white cream he was using. I had a t-shirt and panties on. My hand went right to my pussy. I was rubbing it feverishly. I orgasmed right away, then I could see him start to thrash around a bit and he started groaning. Then he came in huge spurts all over his belly. I came again very hard, and a moan slipped out and I thought he might have heard me. So I ran back to my room and jumped into bed. I was shaking from my orgasm still.
I then heard him walking down the hall, he knocked lightly and opened my door and asked if everything was ok. He came into my room wearing just his robe. I said, 'Yes, all was fine.' He smiled and patted my leg. I was so wet and I could smell the hand cream he had used for lubricant. Then he left.
I fingered myself to two more great orgasms, just thinking of him. The shows continued at other times. I'll tell you about them next time.