I'm really glad, just on a LBS level, that you "read him the riot act" with that email. Sounds like he had it coming.
I have only two quick comments/suggestions for you:
1. If he didnt already understand: make it clear to him, that his mistress called YOU, not the other way around. Offer to prove it, if you have means of doing so like a callerID log.
2. Avoid useless or self-hurting questions. "Why did you lie", is a useless question, There is no way you can reasonably expect any kind of useful answer out of that. You didnt even technically know that he lied to start with. But even if he did... what did you expect to achieve by asking the question? Avoid non-productive questions. they only stir up drama
oh, and PS: sounds like, in reponse to your son's counsellor's questions, that he WAS "abusive" towards you in your marriage. It might be interesting to talk with the counsellor, and describe in unbiased, strictly factual terms what was done, and get that person's take on it. If they say "yes"... then the next time your H rants at you about "always painting him as the bad guy", etc, etc... simply point out, that you told the counsellor that he did A, B, and C, and that according to [him/her], that is abusive. SO yes, he IS "the bad guy".
My current status: june 2006. Wife ran out and filed D. Finalized Jan 11, 2010, after 12.5 years M. 3 wonderful sons caught in the middle