About five months ago my husband and I shared a cabin with my sister and her husband for a week. On the first night we were there we all got very drunk and started playing strip poker. This was unusual since we are normally pretty conservative, but we were having such a good time we just said, "Why not." It took a some time but we all got down to just our underwear and my brother in law actually ended up losing the last hand and had to get naked, exposing his wonderfully big cock for all to see. I had always been a little curious about it since my husband is only average size and from talking to my sister I knew it must be bigger. My brother in law has always had a reputation as a ladies man and has even tried to flirt with me on several occasions. I know he saw me staring at his penis, which made me turn red and also saw him ogling my breasts, which are somewhat bigger than my sisters. We giggled and talked about it for a while as it was all completely innocent, and then retired to our separate bedrooms to be with our own spouses. Well my husband needs about half a beer to get drunk and he fell asleep within a few minutes after retiring much to my disappointment. I was horny from all the sex talked we'd been doing while playing strip poker and because of my brother-in-law's big cock, and was really annoyed that my husband had deserted me. I even tried to masturbate, without success. Finally I went to the kitchen for a snack, still in my panties, and while I was bent over looking in the fridge my brother-in-law came up behind me and put his cock right up against my ass. I jumped a foot, turned around to see naked. He put a finger to his lips and went, "shhhhhhhhh." My eyes were drawn to his penis hanging there. And while I just stared at it he suddenly bent down and kissed me on the lips. It must have been the alcohol because for some reason I responded and kissed him back not making a sound or thinking about the consequences of what I was doing. I was really surprised at myself for reacting this way because I've never considered being with anyone other than my husband, let alone my brother-in-law. As we stood there in the darkness with our tongues intertwined he reached up and started lightly caressing my naked breast. I moaned in delight and touched his penis in return, moving my hand along its length. At that point I never imagined anything more would come of it thinking what we were doing was still completely harmless. Suddenly, he stopped and pulled me along with him into the living room and pushed me down onto the sofa. Kneeling next to me I gasped as his hand ran across the shiny silk of my panties and tightly cupped my pussy. 'Oh, God,' I thought, 'I'm so hot!' His fingers slid up and down between the folds of my cunt and my hips began to undulate slightly. 'So good, so good, please don't stop, please, please!' He reached under the waistband of my panties and found that I was very wet, he began rubbing my clit in circles until I was gasping for more. I can't remember ever feeling so hot before and forbidden aspect of what was going on, knowing what we were doing was wrong made me even more excited. The fact that our spouses were just on the other side of the hall made me hornier than ever and I became lost in the sensations. Before I realized what was happening he'd moved between my legs, tugged my panties to one side, and had started pushing his now very hard big cock into me. When I realized he intended to fuck me right there and then I was shocked and began to protest and tried to push him off. I knew that this was going too far. Unfortunately, I was very wet by then so when he pressed the big head of his monster against my slick opening he just sunk into me easily with a quick thrust forward. "Nooo!!" I tried to whisper in his ear, but I was pinned under him against the couch. I just couldn't stop him and froze as he continued pushing and working himself in and out of me. Finally I felt his pubic bone grind firmly against mine and realized his big cock was completely buried inside me. "Oh Laura -- I just want to feel myself inside you for a minute -- Oh god you feel so good! Oh yeah!" he whispered into my ear as he started thrusting into me completely ignoring my protests. At that point the feeling was just too good to stop him as immense pleasure flowed between my legs as I had my first orgasm. I was so turned on I couldn't protest any more. I was finally getting what my body needed. He was thrusting in and out of me and I realized I was responding and fucking him back by rocking my hips and pushing back up to meet each thrust. We fucked without a sound until we got into a rocking rhythm that I can only describe as incredible. It was a wonderful feeling to have such a large cock inside me for the first time. I came several more times within a few short few minutes from our first contact and the orgasms were just as intense as the first time. I was dripping with perspiration beneath him almost unable to breathe. Eventually his thrusts quickened and I knew he was going to cum. Then he grabbed my hips and his body stiffened, pushing firmly against my pubic bone for maximum penetration. I reached up grabbing his ass and closed my eyes. Groaning softly, I felt his body shudder as he began ejaculating his sperm inside me. It actually startled me when he let go because I could feel his penis pulse and then a strong spurt causing a pressure sensation against my cervix. Only then did I think about the fact that my husband has always taken care of our birth control by wearing a condom. I have never had to even think about it. To make matters worse I was probably at the worst time in my cycle and realized I could easily get pregnant by our little affair. But it was too late. I just froze, marveling at the feeling of what was happening inside of me. Each time he spasmed I could feel him release another flood deep into my belly making my vagina immediately go slick with our mixed fluids. It was indescribable. I couldn't believe there was so much of it. For a full thirty seconds I felt his pulses while he grunted, pumping his load into my womb before finally collapsing on top of me with his cock still buried deep inside me. As the waves subsided, I lay there in a dreamlike state feeling the heat of his sperm spreading out into the depths of my body. After a few more gentle thrusts he stopped, panting rapidly from the exertion. Finally he pulled his shrinking penis from me and it was over as quickly as it had begun. We kissed lightly and each slipped quietly back to our rooms without a word. As I carefully slipped back into bed next to my sleeping husband I immediately started feeling guilty about what I had just done and also realized I now had a river of semen literally pouring from my open vagina into my panties, running down the inside of my thighs and puddling on the bed beneath my bottom. My sister had mentioned to me when her husband ejaculates he squirts a big load making quite a mess to clean up afterwards. And boy was she right. Now I could feel his wetness all over inside me and pouring from me as I lay there and realized I had millions of another man's sperm swimming inside my fertile tummy, perhaps already starting a new life there that should have been reserved for my husband. My God, I'd just mated with my sister's husband at the peak of my cycle without protection, what had I been thinking! Even gravity in the position we were in bent over the couch increased the odds of conception. Needless to say I ended up crying myself to sleep that night thinking about the possible outcome of our foolishness. The next morning I had to quickly change the sheets to hide the evidence before my husband noticed. Now five months later the only proof that these events even happened is my bulging tummy, now very pregnant with what I know is my brother-in-law's baby. I still cannot believe that I did it. Whenever I see him now he just pats my growing tummy and gives me a sly wink. He knows I'm having his baby from that night and I think he's actually proud of it since my sister is now pregnant too. The only thing I can do is hope our baby looks like my husband. It would kill him if he knew that I'm really pregnant by another man. I didn't mean for it to happen, it just did.