I've been with my wife since we were 18. She doesn't know that since I was 19, I've been fucking her older sister's ass regularly. It started one night when I was at my girlfriend's house. She (31 at the time) stopped by and asked if I could stop by her apartment and help build a new table she got from IKEA. I agreed and she joked that we were going to have a romantic night together.

When I got there later that night, she was on the phone with her boyfriend, who was out of town visiting his family. She pointed to the boxes and I got to work. Not long into me building the table, they began to argue and she hung up after calling him an asshole. She came to the kitchen and we started chatting. She apologized for arguing with me around, I brushed it off, then we began talking about random stuff. Eventually the conversation moved to her sister. She told me that my girlfriend talked to her a lot about sex and that she heard stories of the stuff we've done. I got nervous.

She told me that she thought the stories were hot and she admitted that she felt kinda jealous. I asked why and she told me she'd always wanted to try anal but was afraid of the pain. Only recently had she asked her boyfriend to try but he, for some reason, believed that anal sex, even with a female, would be a gay act. I laughed thinking about that and remember blurting out that she should have come to me first. I remember how serious she suddenly got. She said, "I'm coming to you now. ' We both sat there for a moment in silence. I thought I was hearing things. She followed up with, "Do you want to? "

I stammered, but managed to get out a simple, " Yeah. "

She grabbed my hand and lead me to her room. She took off her jeans and crawled onto her bed. I was in awe. I had always thought she had a nice, big ass, but seeing it unclothed and her black thong disappearing between her cheeks was a perfect sight. I started to undo my pants but she told me not so fast. I had to work her up to it. She told me in a playfully seductive way, " Eat my ass". I didn't need a second invitation. I pulled her thong to the side and buried my face in her ass. I could have spent all night sliding my tongue in and out of her delicious hole. She would moan and grind against my face.

The moment finally came. She handed me a bottle of lube from her nightstand. I undressed, lubed up my cock, and slowly guided it to her ass. I pressed the head into her hole. She gripped and bit down on her pillows. I still remember how tight it was. She let out a few pained grunts as I pushed in a few more inches. I slow began to pull out and push in again. Her grunts lessened. After a few minutes they were replaced entirely with moans. I sped up and began thrusted with more force. I moved my hand to her wrists and pinned them down as I now began to pound her ass. The sound of my pelvis clapping against her fat ass was driving me mad. Before long, I felt my balls tense up as I shoot a large load deep inside her. I collapsed on top of her, my cock weakly shooting out the last bit of cum into her ass, before it too lied limp.

That night started a whole affair between us. She never let me fuck her pussy. I was only allowed her ass, which didn't bother me. Since then, I've fucked her ass on birthdays, holidays, and a few brave times on family vacations. I once even fucked her ass while in the same bed as my sleeping wife. I know it's wrong but I can't help myself around her anymore. The relationship between her and my wife has never been better. They still share stories, only this time my sister in law has her own stories about her mystery fuck buddy.