This just happened yesterday.
Yesterday my wife and I went to her mother's for a Labour Day cookout, which was also a birthday celebration for her mom. When we got there we help set up and make things ready. I did the cooking as always mainly cause they like the way I do things I guess. After we had eaten, we started playing cards. It was just my wife, her father, her brother, and I, but it wasn't long before my wife's uncle wanted to join in. When he did they all wanted to play a game I had never heard of and really didn't want to learn, so I bowed out.
Feeling lazy I wandered into the house, which was empty otherwise. I went into the living room and flipped on the games consol. I played various game for about a hour, when for no reason at all I got really horny. Well I listened and could hear them outside (there were only eight people total) and they all sounded fairly busy. Besides, the door was closed and I would hear anyone walking in, so I thought.
Feeling safe I just started to rub my cock through my shorts for a few minutes, to get it hardening up. Then I reached inside and started slowly stroking it. I thought I would just stroke off inside my shorts and that way it would be easy to cover up what I was doing, if anyone walked in. It didn't last long though and two things made me take my cock out. Firstly I am fairly well endowed and my shorts were really making it difficult for me to get a full stroke. Secondly I ended up really getting into it and just thought hell with it, so pulled it out.
After I pulled it out I really started stroking it. I didn't even consider that I had closed my eyes and only opened them when I heard a gasp that wasn't mine. My eyes popped open and my wife's sister was in the doorway, looking right at me. Normally I would only be a little embarrassed and might even try to make something of it, but this was my wife's sister, and her family were outside to boot. If she had got upset or something and gone out to tell them I would have been dead beyond words.
I just looked at her with what had to be shame and fear in my eyes (cause that's what I felt) and just started repeating, 'I'm sorry!'
She just smiled at me, laughed a little and asked, ' What, doesn't my sister take care of you? '
My sigh of relief could have blown over a tree, but I still felt embarrassed, which I hadn't been since I was young teen. I tried telling her that my wife did a great job and it was just that she was busy. I said I couldn't go out there to ask her to come in and get me off.
She just smirked at me and nodded saying, 'Yea, that's true, yea! So what you just got all horny and needed to get off?' I just shook my head yes and shrugged with a silly grin. She got this big smile and asked me 'So ummm, seeing as my sister is busy playing cards, you mind if I help ya out?' I would not have been more suspired if her dog had walked in and started dancing an Irish jig. I shook my head yes again and just leaned back while she walked over to me.
She knelt down in front of me and started caressing my cock real soft. Just running her hands over the head and just behind it. It was incredible and she teased me like that for a while. It felt like forever and all the time she was telling me how she had seen my cock bulging in my pants at times. She said she had always wanted to see it and touch it. She also told me that she knew I had a big dick, not just from seeing the bulge, but from my wife telling her. I didn't know my wife bragged about me like that. She also said she often rubbed off thinking about me, telling me how much bigger I was than her old boyfriend. All the time she was just caressing and teasing my cock head.
It was the first time in a while that I actually got hard enough for my cock head to turn purple and I know because I looked. I was so hard it was almost painful. Finally she grabbed my cock at the base and stroked it really fast. I don't think I lasted three minutes before I blew a really big load. I shot maybe two to three big spurts on her face and shirt. The rest was just big rolling globs that nearly coated her hand. She laughed and smiled as she got up. Then she went to clean off and change her shirt. She also tossed me a rag to clean up with.
She came back and asked me if I would really mind if we played around like that from time to time. I told her no, as long as my wife doesn't find out. She told me not to worry and that she didn't want that to happen either, but just wanted to have someone to sexually play with. At least until she finds her own man. I'll let you know when more happens!