I went to my wife's sister’s to help out in the yard. I got in the house, and there she was in her sleep shirt. Her husband was cutting the grass in the back yard. I could see him through the kitchen window. I slapped my sister-in-law in her butt. She playfully asked me to quit but slapped me back in my butt. My hands reached her hips, noticing the edge of her panties as hers surrounded my shoulders. When my hands were reaching her breasts, she jumped back and ended up sitting on the counter. As she opened her legs, she said she didn't know I knew about my wife and her husband but said she was glad I wanted revenge. I didn't know what she was talking about, but I was already too horny to find out. So, I began to give her oral. When we couldn't withstand it anymore, she stepped down off the counter and bent over it. We were in the same tune, so I had sex with her as we both watched her husband cutting the grass. I didn't ask her about what happened between my wife and her husband, but it wasn't hard to imagine him making love to her. I didn't ask my wife, either. The image of my wife doing her brother-in-law makes me extremely hot when I have her.