Are you saying you never mentioned her affair at MC?
Yes, we did. However, the counsellor didn't probe this at all. I was expecting to be challenged regarding the root causes of the affair, but it never happened, and our sessions deteriorated into a nice chat.
As I've already said, there's so much good sense in the replies that I don't really know where to start. I'll give a little more detail, but it won't be very coherent.
(By the way, I'm in the UK - northern England - in case that's relevant re law/terminology etc.)
After the affair came to light, I got a message from the OM's wife calling me a wimp and saying my wife had been in touch with her several times - presumably begging her not to tell me about the affair. Until now, I've never seriously considered exactly how the affair ended, but now I think the OM's wife found out and made his life hell. In other words, my wife didn't end it voluntarily.
I also got a message from the OM which, I'm beginning to realise, has been a source of trauma for me. It contained three things: an accurate description of my sex life with my wife (that my wife had obviously discussed with him - and in our bed - and what she said clearly wasn't complimentary); a description of the sex he'd had with my wife, which tallied with the emails I'd read; and an accusation that my wife had had another affair previously. Because the first two things were true, I've tended to believe, or at least found it difficult to disbelieve, the last thing, the accusation of another affair. I also now realise that my wife brought a man who wanted to harm me psychologically into our marriage: having another man describing my sex life to me, and comparing it with the sex he had with my wife, has made me bitterly jealous and unhappy - but, strangely, this didn't even bother me that much until very recently: I guess I worked really hard to supress that, which probably explains why my recent depression has hit so hard. She doesn't know about this message: out of loyalty to her, I never replied to any messages, or pursued evidence of the supposed other affair. I regret this now.
After the affair, we had several instances of damage: our satellite cable was cut, my wife's tyres were slashed, we had stuff thrown at the house. The OM harassed my wife and intimidated her, and was arrested, but not charged. He made up a ridiculous allegation that my wife had vandalised their garage door (no evidence: he claimed he'd cleaned it off.)
A few days ago, I had a short one-to-one telephone appointment with a marriage counsellor (Relate, the organisation in the UK.) I didn't have time to give her the full story, but I think she was horrified by what she heard: the affair, the enforced celibacy. She said I absolutely must talk to my wife about this.
I'm feeling very discouraged at present but I am trying to move forward and to take things one day at a time. I sincerely appreciate all of your comments. I'm really grateful to you for taking time to help a guy out! I hope I'll never need to pay it forward, but I fear I will....