We attended Retrouvaille, and had several MC sessions. Never did get to the whole "infidelity" topic in the MC; we stopped going to her after just doing the basic "here's some homework about what the two of you can do as a couple to meet each other's needs more" standard stuff.
No, it was mostly our own hard work, and that view that you get from the precipiece (sp?), and you VOLUNTARILY step back from it, and say "I don't want to go over this edge." Having faced it, and realizing "I'll be okay with this (if we divorce)," I think made me not WANT to . . . if that makes any sense?