It happened before I met my wife, I met co-workers at a bar for drinks, one of the girlfriends brought a friend who I hit it off with. Long story short she takes me home and fucks me hard. After we finished a guy walked in and looked at us. I asked who's that, your brother? She answered no, that's my husband but don't worry, he's always fucking other women but tonight is my turn. It was my first exposure to an open marriage, I thought it was going to be my funeral. Luckily it wasn't and the wife told me she wanted more sex with me as I was a better fuck than her husband. I never had a clue she was married. I was much more cautious after that.