I think my counselor did a lot to help me break through the denial or the illusion I was under. When I first made an appointment I told her I was questioning my marriage. Then as we talked I told her about the communication with the OM. This was shortly after I had met up with him in my home town. She was very non-confrontational, non-judgmental as good counselors are, but she did say right away that it seemed like I was having a midlife crisis. She also reflected back to me a lot of what I was saying and when I heard it that way I realized how ridiculous it all sounded. She also talked about how people leave their marriages all the time in search of greener pastures and they seldom find themselves any happier and often alone and with nothing. She reinforced that I barely knew the OM... which by the way I was fully aware of and not in denial about. Later she advised me to read some books about why women have affairs. I felt indignant at first when she said that because I didn't really think I was having an affair. But then as I thought about it, it wasn't exactly just a normal friendship and I was thinking about sex with him even if I wasn't doing it. It was consuming my thoughts.
If we compare MLC to addiction, denial is a big part of addiction. You have to deny and rationalize to keep doing the addictive behavior. You like the addictive behavior and get pleasure out of it so you want to deny that it's not good for you and rationalize doing it, even if you know deep down inside that it is wrong and not good for you. When someone is addicted say to alcohol or drugs, the worst thing you can do it beat them over the head with statements like " You are an addict and you must stop." That only increases the resistance. I work with people with drug and alcohol problems and I have attended a lot of training about working with resistant people and Motivational Interviewing. Generally it means using reflections, and telling people what you hear them saying and pointing out indiscrepancies. For instance. "You say that alcohol is not a problem for you but you have this lengthy rap sheet and all of it involved alcohol use." It doesn't always break through the denial, but it works better than being overly confrontive. Denial can be pretty powerful.
I don't know if what works for drug and alcohol addictions would work for MLC. I may be comparing apples to oranges. Shepherdess and SB1 may have some better advice about how to break through the denial. And from the sound of it your wife was so far into it, there may have been nothing you could have said or done at that point to have any impact. Maybe the only thing that can break through that kind of denial is to live through it and eventually find out the hard way that the man you thought was your "true love" was far from it.
One thing I didn't do was to blame things on my husband. I felt numb to him but I never thought it was his fault.