Yes, my business partner and his wife enjoyed threesomes, 2 males and 1 female. My partner is bisexual, so it was a true 3-some, everyone having sex with everyone.
She then began working late. She then began visiting friends in the evening. Eventually he had her followed and, yes, she was meeting one of the former 3-some participants and having sex with him.
My partner divorced her. I'm sure this is not the usual, but it was shocking to him.