met someone you know who you are

Such an interesting situation. Yes, it is so exciting to watch your wife being fucked by another man.
I too have a similar situation. My wife and I have met a number of guys where I have been in the lucky position to watch her having sex with them. Oh, and the other guys have always been ones who had larger cocks than mine. I get sheer pleasure from watching her being stretched and penetrated hard and deep. And I agree, it is more fun than actually having sex. My only weakness is that I like to enter my wife after she has been with another guy with a large cock. It just feels great to feel how it is after she has been well fucked.
As for cheating on you, I have been through that too - on two occasions. This is real cheating when she did not tell me about it until a good few months later. Of course it was a huge turn-on for me. But I also found that she did not tell me about all she did leaving out details here and there. Only during further talks about it a few weeks later did she add what she had missed out.
Nevertheless, all very exciting indeed.