You have to admit that your wife's question is a good one.
[slightly modified from a MsTara captioned pic ]
My wife says she never cheated on me. Honestly if she did it would arouse me. She cuckolded me though shortly after marriage because I knew if I didn't encourage it, one day this would be the conversation we would have. She would not feel guilty about having sex with other men fulfilling her sexual needs but she would feel bad that she was hurting me by doing it. Lucky for me I'm a good little cuckold.
So we were getting ready for my wife’s class reunion. I asked her “so how many guys at this reunion have seen your tits?” She replied “3 maybe 4, wait make that 5, no 6. Yeah maybe 6 guys. I’m not a slut, I just showed them my tits, it wasn’t a big deal.” Meanwhile I’m about ready to blow a load of cum in my pants thinking of these guys all seeing her tits.
She never asked for your permission to start dating him, but when she told you that he had asked her out, and told you how much she liked him and how attracted she was to him, you had strongly and enthusiastically encouraged her to say yes. And now, you are as nervous as she is -- with both of you hoping the date goes well and that it's just the first of many.