I am 16 and my big sister is 19. When she started going to junior college this year she really started to attract the boys. In high school she only had a couple of boyfriends and none dated her very long. Both of my parents work alot and are gone alot. Cindy never worried much about being naked in front of me and I had noticed her nice tits and that she had shaved her pussy lips. A couple of times I heard her fingering herself and I got hard listening to her and jacked off myself. However, when Cindy had a boy coming over alot last month she threatened me not to tell mom and dad and just mind my own buisness. This guy was a real doofus but he had big shoulders and lots of muscles. One time when they were in her room with the door locked I could hear him moaning and telling her to 'Suck it harder'. The next time I could hear the bed springs bouncing and I heard Cindy squealing and telling him to make her come. Although I had never thought about it before I decided to hide in her closet next time and get an up close look.
Sure enough 2 days later I saw Cindy and Rex pull up in the driveway and I ran to her closet to hide. It only took them about 5 minutes to make it to her bedroom and lock the door. I could hear Cindy flirting with him and telling him she wanted to see his big cock. I heard his fly unzip and then I heard him moaning. When I carefully cracked open the door I could see Cindy's little face full of Rex's cock. Although I thought I had a nice 7 inch cock this guys cock looked twice as big. Rex grabbed the back of her head and started face fucking her until his shaft was dripping with spit. My cock was throbbing now and I began to jack off while watching her give him a sloppy blowjob. As Rex kicked off his jeans he also pulled off Cindy's jeans and laid her down on the bed. Rex started to lick her pussy and she started squealing like crazy. Now I knew what I had heard the other day. I've only eaten pussy once but Rex looked like he wrote the fucking book on muff diving. He ran two fingers in and out of Cindy while sucking on her clit. Then he started sucking hard on her pussy lips like he was trying to tear them off. All this time my sister was going fucking nuts and telling him not to quit. By now I had found a pair of Cindy's silk panties on the floor and I was stroking myself hard and fast. Watching my sister was really turning me on. I swear Rex must have ate her pussy for over 20 minutes and I can't count the number of times Cindy squealed and came. Then Rex stood up and directed his rock hard cock at her tight pussy. As he slid the first two inches of his cock inside of her she began to moan and buck her hips toward him. Rex grabbed her ankles and spread her legs even more while he plunged his cock deeper and deeper. As I saw Cindy getting power fucked by this guy I started to come and just kept her panties over my now exploding cock. I had jacked off with panties before but as I kept the panties over my cock as to not make a mess it felt even better than before. I could not take my eyes off them. Next, Rex asked her to get on top of him and as he laid on his back Cindy climbed on top of his cock. My view was now of Cindy's sexy ass bouncing on top of Rex and him grabbing her ass. I felt my cock getting hard again so I began to jack off again. Being only 5 feet away from my sexy sister and her boy toy made me really hot. After she rode his cock for awhile he asked if he could fuck her from behind. As she got on all fours on the bed Rex got behind her and slipped his cock in her pussy. Rex must have liked this position best because he began to make some twisted faces as he was fucking her harder and harder. Meanwhile Cindy was loving it and she began to rub her tits and squeeze her nipples. Cindy told him he was making her come and he just thrusted into all the harder and smacked her pretty ass. Cindy moaned and moaned and I was turned on to see that my 'innocent' sister was now down and dirty and multi-orgasmic. My cock was throbbing again and I wrapped her panties around it again as I felt like coming again. As Rex started grunting Cindy screamed at him to pull out and he did just in time to squirt his hot load all over her back and on her ass. I had never seen another guy come before and seeing his cock covered with Cindy's pussy juice and then seeing him blow his load made me come again. Rex took his time and just rubbed his still hard cock against Cindy's sexy ass. Cindy was too tired to get up and told Rex what a great fuck he was. When Rex got dressed and left Cindy got up and went in the bathroom giving me a chance to escape her closet. I slipped out and ran to my bedroom and put on a pair of boxers and a t-shirt. 10 minutes later Cindy knocked on my door and as she came in she asked me how long I had been home. I told her I just walked in as Rex's car was pulling out and I asked if he was mad at her. She stated no he was just in a hurry to get home. Cindy did not know that I watched her getting fucked and I am already planning to sneak in there and watch her again!!