I am a horrible person. I know that. What I did was wrong, but it felt so incredibly good. I feel guilty every time I think of it, but that guilt doesn't stop me from getting wet or wanting to do it again.

My sister and her husband own a lovely lake-front home that's an hour away from the college I'm going to. On weekends, I would often go and stay with them just to get away from the campus for awhile. I'm very close with my sister, and I always liked her husband. He's a kind man who's very protective, and the two of them have done a lot for me over the years when my parents fell through. Last spring break, they invited me to stay with them for the week and enjoy the lake during my holiday away from studying and tests.

On the second day, my sister was at work but her husband was off. His job requires shift work, so he'll be there for twelve days and then gets seven off. I went out to the garage to put a load of laundry on and he was out there working out. He said a polite "hello" and then went about his business. I'd never seen him like that before, but he was shirtless and glistening with sweat, and his body was chiseled from rock. I couldn't stop staring, and he didn't notice. I threw my laundry in and went back into the house. About an hour later I heard the shower go on, and fantasized about going in and taking a shower with him. I felt guilty about the fantasy, but assured myself that's all it was.

The next night, after my sister had gone to bed, I found her husband watching a movie in the living room area, drinking a beer and kicked back on the couch. I sat on the other end and asked what he was watching. He caught me up on the details, and offered me a beer. By the time the movie was over, I was buzzed, and we were chatting about our lives, our troubles, college, and all sorts of things. We were sitting awful close at that point, and I could feel a strange tension building. I leaned in and kissed him, and he kissed back.

Now I should say that my sister and I are very different. She's short and buxom. Big tits, curvy hips, and muscled like a cheer-leader. I'm quite the opposite in most respects. I'm taller, leaner, small tits, but a big round ass from years of playing softball that draws attention anytime I wear anything tight. I couldn't understand his interest, being that my sister was ten times the looker I was, but I suppose it was that very difference that drew him in.

Before I knew it, he was peeling my shirt off. His lips and mouth were all over my neck and he unhooked my small bra and tossed it off like a man possessed. He pushed me onto my back and suckled at my little pink nipples, and I wrapped him up with my long tan legs. He seemed to realize himself and started to pull away. "We can't," he said. "We shouldn't." he said. I reached down and grabbed his rock hard cock through his pants and gave it a light squeeze, and he shut his eyes and bit his lip. He didn't move, but he didn't come back to me, so I unbuttoned his trousers and peeled down the zipper. He was wearing nothing beneath and his long thick cock sprang out. It was a sight to behold. I could see for certain yet another trait that my sister found wonderful in him.

Before he could protest, I slid down so that I could take his cock into my mouth. I skirted my lips with my hand so that he couldn't tell where my mouth began and ended, and fought to take as much in as I could. My jaw felt as if it wasn't going to break as I tried to drink him in. He groaned with each stroke as I bobbed my head, pistoning my lips around his length. I felt him reach back and lay his hand between my legs, and he started to rub against my pussy through my shorts. I was already hot and wet, and I was sure he knew by the way I moaned around his cock. I pulled my lips free and told him to lie down.

When he did, I stood up and peeled off my shorts and panties. I turned so he could get a good look at my round ass and threw a leg over him. I lowered myself so I could suck his cock and pressed my pussy flush against his mouth. His hands filled with my ass cheeks, he lapped at me like a wild animal, and I struggled to take him deep into my mouth. With wild abandoned we worked each other until we were in a frenzy. When I pulled free, he started to protest again, saying this wasn't right and that we shouldn't and that he loved my sister and they were married. I was lost to my lust and I flat out didn't care. I wanted to fuck him. He was going to fuck me.

I straddle his hips and put a finger to his lips. Reaching down between us with my other hand I lifted his rock hard cock so that it's head nestled just against my wet hole. I pressed my hips down and took just the tip into me and his head rolled back and he groaned like he'd never been inside a woman before. I rolled my hips for a solid minute until I worked half of him in, and at first it felt like I was being split in two. He was so thick I was sure I couldn't take more, but as I began to slowly build my rhythm, the pain gave way to pleasure. I leaned forward and shoved my tongue in my mouth, and he gripped my ass tight, pulling them apart. My clit was grinding into his flesh as I took as much of him inside of me as I could, and I felt his finger brush against my asshole. I moaned, and he took it as an invitation. Strangely, he didn't force a finger in like most men try. He simply rubbed his finger against my wetness until it was moist, and then put a little bit of pressure against my tight little button hole. Then he moved it in a tiny little circle, and the feeling was amazing. I couldn't stop the build of my orgasm, and I came so hard I had to bury my face in the couch pillows to keep from being too loud. As my orgasm subsided, I fucked him long and slow, savoring each stroke for it's intensity. His cock was pulsing, and he kissed me deeply, his hands running through my hair. I shivered, and could feel goose bumps rise all over my skin.

"From behind," he said quietly. "Please." He didn't need to ask more than that. I stood, pulling his cock from me, and got down on the floor in front of the couch. He kneeled behind me, cradling his erection into my waiting quim. He dug his hands into the flesh of my big round ass and pushed into me so deep that I gasped. Then he pulled nearly free and thrust himself almost completely into me. My entire body rocked as he began to fuck me, and I reached between my legs to play with my own clit. It was almost painful, but the sensation combined with the tickling on my clit became more than bearable. I began to realize that my sister could catch us any minute, and from there, I had a strange thought. In my mind's eye, I could see him fucking my sister like this. Her face contorted in pleasure, her big tits swaying as he pounded her from behind. It turned me on to imagine them fucking, and I was sure I'd be able to cum again. Still, I knew it was risky to go on to long, and as he pounded away, I wasn't sure he was close enough. I turned and looked over my shoulder, my mouth a perfect O shape as I cooed. When his eyes met mine, I decided to help him along.

"You like that pussy, baby??" I asked. He nodded. "Fuck that little pussy. Fuck MY pussy." He moaned, his eyes still on mine, and picked up speed. "Come on," I coaxed. "Fuck me baby. Fuck that tight little pussy." I was pulling out all the stops. I'd never talked dirty before, but it was turning me on just as much as him. "Fuck my tight little slutty pussy!" I cooed, feeling another orgasm building as I watched his pectoral muscles tense as he pulled me into him by my hips. "Fuck me!" I commanded. "FUCK ME!" I shouted. I felt him tense and try to pull free, but I was orgasming too. I pushed back against him as he tried to withdraw and he toppled to his ass. I pushed up on him and rocked my hips faster and faster. He tried to push me off but at the angle he was, he could get no weight behind him. "No!" He said, even as I felt his cock spasm inside me. I felt his first hot gush spatter inside of me, and it pushed me over the edge. I came hard as he began shooting thick spurts inside of me, and he was desperately saying "no no no" even as he came. When we finished, he collapsed onto his back, and I pulled my pussy free. I was dripping wet, and his cum leaked from my lips. He looked absolutely disgusted with himself, and when I went to kiss him, he turned his head.

"This is completely fucked up," he said. I tried to assure him that everything was fine. That we were just human beings caught up in the moment. He was pushing me away and I was trying to comfort him. He got away as soon as he could, and went for a shower. I cleaned up and got dressed, then went to bed.

Since then he's been dodging me, but I've kept the secret. He doesn't say much to me when I visit and he won't allow himself to be alone with me in a room. I've tried approaching him and he gives me a few short words and then walks away. I want him to know that I'll keep the secret. That I won't ever tell my sister. That it was the best sex I've ever had and that I'd love to do it again anytime he's willing. But then I see my sister's face and how proud she is of what I'm doing with my life, and I feel horribly guilty.

I'm a terrible person. I know that.