Listening to someone fucking at a party and it turns out it's your wife

Description: 

You go to your friend's place for a party. You go to the toilet and on the way back you hear moans coming from one of the rooms, it's pretty hot, so you just listen.

Your friend comes to see where you and the others have got to and once he hears the moans from the room, with no hesitation he opens the door and asks if he can join in and this is when you see it's your wife making those noises with another man.

In shock you don't do anything, you just stand listening.

The door opens and your friend joins at around 5:20...