Personally, I could never be in that situation. I'm actually quite amazed that both you and your friend's wife are perfectly fine with this happening. With that being said, can you really be upset or hurt about something you allowed to happen? That's like me allowing my bf to go out and cheat and then get mad when he actually likes the girl. I hate to say it but allowing your relationship to get to the point where everyone is sleeping with everyone.....that is going to happen. I personally don't think you can complain when you openly allow your wife to go out and sleep with another man and not even care.