My god Leslie, I feel so terrible for you! regardless of whether things have gone further than flirty emails, the fact that you found those emails in the 'trash can' shows that he is being sneaky and hiding stuff from you. His wife. From whom there should be no secrets, esp ones like flirting with girls you specifically told him to stay away from.
I agree with everyone else that you should seek counseling. You guys can't get through this alone - your trust in him is crushed and he could possibly have some issues where he needs attention from other women, both issues CAN be helped with counseling.
My heart truly goes out to you and I hope you can happiness again. big hugs.