My wife's twin sister came to stay with us for a few months after a bad breakup. We have always had a brother sister type relationship. At least as far as having any interest in each other goes. We've gotten drunk and flashed each other a few times but my wife was present and knew that it was harmless and that nobody was going to remember it tomorrow anyways.

While she was staying with us, she was a guest getting prepared to go back on The dating market. She would lay out in the sun in a very small bikini in the backyard. Some days my wife was working and I was not and I would be here to witness it.

On this particular day she fell asleep in the Sun. I was looking out the kitchen window and I noticed that her bikini bottom had slid off to the side and I could see her bits. Now obviously being my wife's twin it looked exactly the same. But for some reason on this day I decided to whip out my dick and start pleasuring myself while looking at it. She had not moved in quite some time so I was pretty confident that she was sound asleep. I stood there in the window with my pants around my ankles beating on that thing and she sat up and looked right at me. I immediately moved away from the window tucked myself back in my pants and tried to pretend like nothing happened.

This was 2 years ago and still to this day neither of us have said anything about it. I've gooned over the thought of it again and again. I can only assume that she had to have seen it all as I was in full display in front of a wide open window.