Yeah, I feel exactly the same way. Even before it turned physical, he apparently was confiding in her about all the problems in our R that he refused to talk to me about. I also got told everything was "fine" a lot.
If your H has always been telling the truth and it never was anything physical, I'm sure he doesn't see anything wrong with it. He probably sees it the same as confiding in any friend, regardless of their sex. That's one reason I suggested he read that, maybe he would understand why you feel betrayed.
But you know the situation better than anyone, and if you think he wouldn't listen/accept what he read, then there has to be a different strategy to try.
I know I've benefited from the couple times I've talked to my school counselor, she helped me see some of my biases and clarify my goals and gave me some insights into my H's behavior. I haven't really felt the need to go back since I get a lot of that here on the BB, but if my H wanted to R, I'm sure I'd be an emotional mess for a while and would probably want to talk to someone about it.
In other news, TGIF!!!!
Michelle - Proud DR Rockette S: 28JUL07, D'd: 29OCT09 http://tinyurl.com/27j9qo2