[MF] [MF] I heard my sister having sex in the other room, and it turned me on

I’ll try to make a long story short. My wife and I decided to have a very small gettogether at our condo on New Year’s Eve. We only invited two people: my sister and a friend of mine from work. Both had been COVID tested very recently, and we specifically chose them because my sister is single and lives alone, and we didn’t want her to be alone. And my friend is also single and lives alone, and he has some on-and-off issues with depression and anxiety; nothing too severe, but I feel bad for him because he’s a really nice, humble guy. He’s the shy introvert type, so I thought it would be good for him to have a fun night over at our place without too many people to make him anxious.

The night turned out to be a blast. We were all drinking pretty heavily, watching movies at first, then socializing and playing cards and listening to music, stuff like that. Everybody was enjoying each other’s company. The drinks were still flowing after midnight, and my friend was coming out of his shell. My wife and I both noticed an hour or two prior that there was chemistry building between him and my sister, and it was getting more and more obvious. A little later on at around 1:00 a.m., my sister approached my wife privately and said something about how she was pretty sure something might happen between her and our friend that night, and my wife wasn’t really surprised at all because she saw it unfolding a few hours prior.