My wife was out of town with our two boys. She had arranged for her younger sister, Kitty, to spend the night at our house while her apartment was being painted. My wife and I had a great marriage, so I guess she just naturally felt nothing would happen between me and her sister. Her sister bunked out on the sofa, and I went to bed. A little later, I looked up toward the bedroom door and there was Kitty wearing just a t-shirt. I could plainly see her shape under the thin material of the shirt. I got out of bed and walked over to her, nervous, not knowing exactly what she wanted. Throwing inhibition aside, I began to lift her t-shirt. To my amazement, she didn't resist. I slid the shirt over her head, and she immediately grabbed my boxers and pulled them down. Even though I love my wife, the sex Kitty and I had that night was incredibly strenuous and exciting. We've been meeting to do it for about a year now.