I caught him cold!
I'm 20 now but when I was 15 this happened. I was from a broken family with mom and dad getting a divorce when I was six. Some years later, mom remarried another man who was also a divorcee. Her new husband had a son named Nick and he had lived with his dad most of the time.
When this happened, Nick was 18. Nick was over 6' tall and very muscular. On this day I got home from school and didn't think anyone was home since there weren't any cars at the house. So I took the shortest route to my room. This sent me through Nick's room. I opened the door and walked right in. Then I had the shock of my life. Standing in front of his mirror with his pants dropped around his ankles was Nick. He had his hand wrapped around his erect penis jerking it off! I froze in my tracks with my mouth wide open. Nick couldn't hardly do a thing in the position he was in but stand there looking at me in the mirror. I said 'My gosh, I'm sorry'. I also noticed the pictures Nick had in front of him on the table there and it looked like it was pictures of naked girls.
I should had turned around and ran out but I guess I was fascinated by what I was seeing. Especially with that big thing Nick had in his hand. I then asked Nick 'can I watch'? Nick said 'well, you've already seen it so you might as well'. I moved closer to Nick for a better look. I looked at the pictures. They were all of these beautiful naked girls laying down with there legs spread showing there pussies. Nick's hand was covered with a cream of some kind. He went back to jerking off while looking at the pictures. Nick then went to shaking some, groaning and then started thrusting his hips. His head went back and he let out a loud aaahhh as the first shot of cum came out his penis hitting the mirror. When I saw this I said 'Oh my'! I'd heard about boys doing this but seeing it happen was still a bit of a shock. He continued to shoot his cum around three more times before finally just dripping on the table top.
This ended up being our first time. Nick and I then often got together in his room before my mom and his dad got home. I'd masturbate my pussy in front of him and we eventually started doing it to each other. Nick wanted to put it in me all the time but I wouldn't go that far. So, he'd run his hands all over my body and then would shoot his cum on me. He loved doing this especially on my tits or on my legs while rubbing the head of his penis on them as he came. I'd end up having to shower when he did this.
Well, we're now grown and Nick is married so Nick is now getting to do that thing he so badly wanted to do with me. As for me, thanks to Nick, I sure knew how to make my boyfriends feel good and have them make me feel good in return. Maybe I should had let Nick be my first since I've never found another boy or man that was as big as Nick's was and I've always wondered what it would had felt like in me.