It's the deception behind the action. Why men deceive, why did mine?

My husband cheated on me with a younger woman. He is her boss and he is also my boss, we work for a human service agency. Yes, I humane of him! Anyway, years ago he started chatting behind my back with women on the internet and started a relationship with someone on the internet and they would exchange phone calls and letters. Him and her ended their relationship before they actually met in person, but he always told me, " I never slept with her, so I did not cheat." When I went for therapy regarding his recent affair, the therapist told me its the deception, not the fact that he did not sleep with the person he met on the internet years ago. Why the need to decieve? Someone I know goes to strip bars, but he does so deceptively. He hides it from his wife and says no harm because he does not sleep with any one, but I say its the act of deception thats wrong and he knows it would upset his wife, but he does it anyway behind her back. What do you all think?