I caught my Step-sister

I was 15 and my step s****r was 18. One night I stayed up late in the living room playing Xbox. It was about 1 am. I decided to go to bed. My room was right beside her room. When I walked by her room, I heard moaning. The door was cracked a little so I peeked in to see if she was okay. All I could see was her bouncing up and down, naked. Her big boobs going everywhere. I couldn't see if she was having sex or not. So I slowly walked in, making sure she didn't notice me. I opened the door just enough so I could slip in. she didn't notice me. Then I saw she was bouncing up and down on a guy's cock. she came up to where it was just out of her pussy and then all the way back down. My cock got so hard watching her. I took it out and started jacking off. She was so hot.(Still is) After cumming on all her stuff for the pass year. It was amazing to see her being fucked. I wished it was me inside of her. She bounced on his cock for a few minutes. long enough for me to cum. as I was cumming. I made a noise and she looked right at me. She wrapped herself up in a sheet and came over to me. She was mad and embarrassed. She asked me how long I was standing there. I said only a few minutes and then she saw her cum covered shirt in my hand. She turned red. I said I was going to tell mom she was have sex. (Mom told her she couldn't have sex until she was married.) She begged me not to tell. I said "lets make a deal then. I want to touch your boobs." She said,"hell no." "I'm going to tell mom." She finally gave in to me, because she didn't want to get into trouble. I reached up with both hand and grabbed two D cup boobs. they felt amazing. Very soft and squishy. She took my hands off and said, "that's enough. so you're not going to tell mom." I said " That wasn't the deal, I just wanted to touch your boobs." She said angrily " Then what is the deal?" I said "Let me touch your pussy." As I was reaching my hand between her legs, she garb it and said " NO, NO, NO, I can't let you do that. You can tell mom if that's what you want." After failing to touch her pussy, I said " the deal is, you have to let me watch you have sex when I want to and that is the only way I want tell mom." She said "Fine, but you have to be somewhat hiding and you can't cum in my clothes." "That's a deal." So I sat in the closet with a perfect view watching my Step-s****r getting fucked. The guy she was having sex with was my next door neighbor. we use to play Xbox together. He was pretty cool. for A few weeks after, I didn't see him in her bed. I went over to his house to see if he wanted to play Xbox. After we played games for a few. I asked him if he was dating my step-s****r. He said no. I told him how great it was to see her being fucked. He said I would get to fuck a girl one day.(he didn't know I had sex with my mom). I agreed with him. I also told him how much I really wanted to fuck my step-s****r. I told him about a porn I watched where the boyfriend blindfolded the girl and he let another guy fuck her without her knowing. He said he seen it too. I asked if he would try it with me. I wanted him to blindfold my step-s****r and after a little bit of them fucking. He would pull out and let me in. He said no, and that I would get caught. I said I didn't care and offered him $100. I have been saving it, but it's worth it to spend it on that. He said yes. This is how we did it. It took him a few days to get her to agree to have sex with him again at my house. He told me to wait a 15 minutes after they when in the room. I stood by the door. My cock was throbbing. It hasn't been that hard since I had sex with mom. any ways, after about 10 minutes I heard him ask about the blindfold, she said it was cool. I started rubbing my hands together to warm them up. I rubbed my cock also. After 5 minutes, I walked in slowly, he looked at me while he was fucking her and was moaning, so she didn't hear me. I got naked and stood beside him as he was sliding in and out of her pussy. it looked so good. he did a few practice runs, he pulled all the way out waited a few seconds and then pushed it in. after the fourth one he nudged me to get ready. Here was my chance, I was going to fuck my Step-s****r. I only dreamed that this would happen and now it was going to. He pulled out and backed away and I stepped up and put my cock in her pussy, it slide right in. Her pussy was so wet and hot. Her reactions started to change a little. He was a little bit big than me. But he started talking to her, like he was the one inside of her. I started to fuck her hard and she was loving it. I fucked her till I exploded inside of her. I bit my lip so I wouldn't make a sound. I made a few hard thrusts to make it seem like I wasn't cumming. Then I waved my neighbor to get ready. I pulled out and he slide in her cum filled pussy and started fucking her hard. It was amazing. We did it a few more times, before she started getting suspicious. I never got caught.