My wife and I had been married a short time. My wife was five foot tall, and a blonde bombshell. When we would go to a party or event men hit on her all the time even with me standing right beside her. We had our own house and I had a cousin who grew up with me living in the same house. He was very close to me as we were close in age. He worked construction and as you can imagine was slim, well muscled and he was good looking. I never felt threatened, and I never saw it coming. My wife and my cousin would often flirt, and I always thought it was fun. He lived only a few blocks from us so if I came home from work to find him there, I never thought anything of it. He was after all family. I was working six days a week and was gone from 7 am to almost 7 pm so him visiting her and keeping her company I encouraged and appreciated.
Things changed when one day saying goodbye he gave her a hug at the front door. When the door closed my wife turned around and said to me that she loved being hugged and feeling his big strong arms around her. I was a skinny five foot ten guy that weighed in at 125 lbs vs my cousin who was about the same height but probably was 175 lbs and was all muscle. Instead of feeling threatened by her saying that I was kind of turned on. I noticed the flirting go up a notch after that and I started to encourage my wife to tease him. One day when we were getting ready for a bar b que we had invited him over for I suggested she take of her bra and wear a tight white t shirt. My wife agreed and seeing his reaction was fun as hell for me. I noticed however at the same time how my wife looked at hm and that night I asked her if she wanted to sleep with him. She said she had thought about it and yes, she did. I told her then let's make it happen. Let's seduce my cousin together for her.