I have watched both friends and strangers fuck Kate, and she has fucked guys during our marriage that I have never met. Kate has sex with friends of mine, husbands of couples we know, casual acquaintances, and strangers. She has been having sex with her older married boss for years.
I find it hot to be around guys, in normal everyday situations, who are fucking my wife, I like being around guys who know that my wife fucks other men and they know from their own personal experience what a hot fuck my wife is. That being said, I also love seeing my wife being a total slut for some total stranger we have just met. It also turns me on when guys I don't even know are fucking my wife.