Gucci, I used to think you knew what you were talking about. Now I think you are a bully. None of us are professional therapists, psychologists, social workers or romantic advisors. And that most certainly includes you. Stuck is right. You have no proof that she is in an affair. You don't even know who she is. Luckily, Orich knows how to stand up to bullies. But I'm sure there are others on these boards who may not be so grounded. You can do damage to other people's relationships by giving them cavalier advice.
As for there being no change in his posts, that is manure. They are signed up and going to Retrouvaille in 4 weeks. That is a huge improvement. They are on a path that leads to reconciliation. However, if he were to become suspicious, accusatory, and belligerent at this point, based on your bogus assurances that she is having at least one, and perhaps several affairs, then he certainly could derail the progress he has made. You should avoid dangerous accusations.