My wife and I had a good marriage, but the sex had declined since the births of our four children. We recently started to sleep in different bedrooms, a mutual decision in order to get better sleep. The arrangement had continued for a couple of weeks when my wife's amazingly hot younger sister, Marianne, came to stay for a month in our guest room. The guest room was across the hall from my new room. Marianne had been married twice before, and this was the first time she had come to stay with us while she was single. I had always been attracted to Marianne but never imagined cheating on my wife. However, trying to fall asleep alone in my room got me thinking about Marianne. I almost had trouble telling the difference between my imagination and reality when Marianne came through my door. She was wearing nothing but a red bra and thong. She then locked the door behind her. I was amazed. I could have stared at her for hours, but she wanted something more. She jumped onto the bed, and we made out for about five minutes. I was tired of waiting, so I passionately picked up Marianne and placed her down on the bed. Then we started to have amazing sex! She screamed and I panted. We had sex until 5:00am as my wife slept upstairs. Marianne and I had sex almost regularly after she had bought a house down the street. We continued to have the best sex for years!