Victory is the Lord's...
Let me tell you a story (a real one). I was about 13 and there was a certain young woman in my church that I looked up to. She was a known virgin, a high school senior who taught us younger ones in Bible school.. One Sunday morning during testimony, she suprised everyone and went up to the pulpit and starting crying hysterically, asking the church to forgive her for deceiving them. WhAT! I was floored... she went on about sneaking off from school with a guy at school, another senior, to have sex in her mother's house! Her mom was one of the prominent women in church..her little girls could do no wrong. She had this thing going for quite a while. And, I later found out some of the folks in the church already knew. That was my lesson on imperfection. I saw her differently, but oddly enough, I also had a lot of respect for her after that day becuause she said the Holy Spirit led her to confess. She was no longer "perfect" she was a human being who happened to love God.
We all strive to be like Jesus, but while in this earthly body, we'll always wrestle with our flesh and will make mistakes. What makes us more Christ-like is the ability to forgive. It's harder to forgive when we perceive people as "perfect." I've had some hard lessons on forgiveness, too! And in the end, I was so glad I forgave. It was a burden lifted off my shoulders and I became a better person for it.
I am truly sorry your friend is dealing with this, seemingly on her own. Hopefully, she and her husband can get counseling. Your friend can't have a healthy marriage if he sees himself as not doing anything wrong. The sanctity of their marriage just doesn't seem to be there.
He'll have to meet her halfway for them to start the recovery process. If they are able to work on their marriage, the victory is the Lord's indeed.
Then, they can look back at this and realize all along that they were making a great testimony for God. I pray that's the end result!