My husband is contantly e-mailing old girlfriends and female clients. Is this cheating?

Almost 3 years ago he did work for a single, very intelligent woman. He would take pictures of her home that were not related to her work. When she was out of the country he would e-mail her daily, once he stated that it was not the same without her there and in another thinking of you lots. In my mind he emotionally cheated on me. He freaked out stating it was only business and I was over-reacting, he them started to delete all of his e-mail and lie about it. When I confronted him once again it was all my fault. He still does work for this client and every time he does I am an emotional wreck. Am I over-reacting?