was it wrong of her

i found out that even though my wife and i have spoken about swinging for a while before actually agree that she had got tired of waiting to meet some one on aff, and decided to find someone on her own
we joined a club together mid sept. and the instructor and her took a liking to each other
she spent the last 5 weeks chating and emailing a gentleman without my knowlege, at first it was friendly chit chat then it got hotter and heavier to where he was in my home without me there and they proceeded to have heavy petting…. him licking her breasts and rubbing her pussy while she was just stroking his cock inside his pants…. she then says that they stopped and nothing else happened..
am i wrong in feeling she cheated on me behind my back..
we are working this out and will still be going to swingers bars together
she has understood that not telling me and doing it behind my back in our home alone was wrong
please let me know if im wrong and what i should be discussing with her
thank you