An old friend of ours that works with my wife came around to discuss the delivery of some furniture I had purchased from their company. We ended up drinking several bottles of wine and eating Chinese together. The evening progressed well, but I had work to do on my computer, so I excused myself and went to the garage/office to get on with it. After a while, I went to go back in the house and thought it seemed really quiet. I crept through the rooms and peeped round the living room door. Ellen, my wife, was laying back on the sofa and so was Rob, our friend. They were kissing and his hand was up her skirt. As I watched, he moved to give her oral. A second or two later, she pulled him upwards and they began having sex. I left the room and loudly came back in a while later.