I live at home with my 49 year old mother and 16 year old sister, I’m 18, and my dad died in an industrial accident 6 years ago. This summer my grandmother came to spend a month with us and my sister had to give up her bedroom and move in with me. That meant she had to share my Queen size bed. Well I like my privacy and I wasn’t too happy about that but I gritted my teeth and accepted it because there was nothing else I could do. I have my own computer set up in my room and at night after everyone goes to bed I like to watch porn. I didn’t know how I was going to pull this off with my sister in the room. After the first night I rearranged the room so my computer screen was turned away from the bed. I always listened with earphones to keep the sound from alerting my mother. Well that night after my sister fell asleep I slipped over to the computer, and making sure my sister remained asleep, started to watch as usual. Making sure my sister was still asleep I jacked off during a particularly juicy scene and after wiping up went back to bed and slept like a baby. This went on for a week or ten days until one night just as I was starting to cum I sensed something was wrong. I glanced over my shoulder and there standing behind me watching was my sister. I quickly covered up and gasped, “Oh sis, please don’t tell mom on me?” “I’ll think about it!” She said and went back to bed. I was so frightened that she’d tell mom I couldn’t sleep. I was on pins and needles all day but she didn’t tell, just looked at me and smiled viciously every time our eyes met. That night after we went to bed I said, “Thanks sis for not telling.” “I may yet, she said, unless we can work something out!” “What do you mean?” I replied. “Well, she said, you have to give me half your allowance and something else.” “Okay, I said, but what’s the something else?” “You have to let me watch at night with you!” “Sis I can’t do that. I replied, It’s nasty.” “Oh yes you can, she said, and unless you agree right now I’m going straight and tell mom!” Well what could I do, she had me, so I agreed. I moved the other chair over by mine at the computer. That night after mom went to bed we sat down by the computer. I didn’t know what to put on so I just replayed the video from last night. She took the earphones from me saying, “I want to hear too!” When it got to the part where I was just about to cum last night she said, “You can do what you were doing last night now.” “I can’t sis” “Oh yes you can she said, and you will!” Well I’d never jacked off before with anyone watching but I took out my dick and started to play with it, and soon it got hard and I started to stroke it and pretty soon I let loose with a big load of cum. “You really liked that didn’t you, and if you want to hear too set up another set of earphones.” What could I say, of course I liked it. As we lay in bed afterwards it dawned on me how hot it had actually been to jack off in front of my sister, and it also dawned on me how much she’d developed and hot she was starting to look. The next night I rigged a splitter on the sound source. As we sat down after mom went to bed she told me to pick something new. Over the next few days we watched a couple getting it on in various positions and when they’d eat each other. I would jack off as usual but I noticed that when I did she would rub herself between the legs. One night just as I was starting to jack off she said, “I want to do it for you!” I was at first dumbfounded but she reached down and grabbed my cock and in what seemed like an instant it was harder than it had ever been. This went on for several days with her sometimes jacking me off twice, and then our grandmother went home and sis moved back into her room. That night I had just turned on the computer when I heard my door slowly open and there was sis, so we proceeded as we had been with her jacking me off every time. By now I had started letting her pick the video some night and every time she picked it was a boy eating his girlfriend’s pussy. One night she picked one of a brother eating his sister’s pussy. Just as it got juicy she grabbed my dick and said, “Before I make you cum I want you to do that for me!” “Sis I said, it’s nasty!” “No it’s not she replied, I just took a shower!” And she went over to the bed, took off the bottom of her pajamas, and laid back on the bed with her legs spread. Well I had no idea what I was doing but since she wasn’t going to jack me off till I did I went over, put my head between her legs and started to lick. Her pussy didn’t taste bad at all and as I licked she put her hand behind my head and pulled me to her. As I licked further up in her pussy I must have gotten to her clitoris because she put the other hand behind my head and began to hunch my face. I must have got her off because she started to moan and her pussy was soaking wet with juice. She then jacked me off and after wiping me off with Kleenex slipped back to her room. We did the same for several nights but when it was my turn the video would be of a girl giving a blow job. Then the night the video featured a sister sucking off her brother I said, “Now it’s your turn!” Well she did but when I cummed in her mouth spit it in a Kleenex. As we watched more and more of this type video she learned to swallow as she sucked me dry. After this we went to the 69 position which was more fun than anything we’d done before. Up to this point we had never actually fucked though I had played with her pussy many times. It was inevitable that we would get to that, and once we did it was every night with all the other things we had done just preliminaries. It was also inevitable that we’d eventually get caught and that’s what happened. I don’t know if we got too noisy one night or if mom just woke up for some reason but I heard my mom scream as the door flew open just as I was unloading a barrel of cum into sis’s pussy. “Oh god!” Mom gasped as she ordered my sister back to her room and sat down on my bed and began to sob. “How could you do this to our family!” She screamed as she started to beat me on my ass with her bare hand. Then she said, “I’m going to sleep in your bed from now on to make sure nothing like this ever happens again, and I just pray God your sister’s not pregnant. And I also intend to punish you every night until you’ve repented of your sin!” At that she collapsed into an exhausted sleep. Although my ass was sore from the beating it had made me enormously horny and I jacked off three times before I woke up the next morning. So that was the way it went from then on. After dinner when sis and I had finished homework she would go to her room and mom would go to mine with me.