First of all, welcome to a2k
Secondly, you were wrong in spying on your wife and
thirdly, you were even more wrong to pretend you're
your wife and chat the guy up.
I can imagine that you probably coerced him into saying
what he did say and now that you got proof that he
had cheating in mind, you automatically assume you're
wife is in the same corner.
Furthermore, you forbad your wife to talk to this guy
again and now you don't know why she's mad?
Everything you possibly could do wrong, you did! Your
wife is a grown woman who can make her own decisions
about whom she is going to see, talk to, or meet.
So far, she has done nothing wrong - nothing at all!