They do if there is guilt or pressure. Are you tell me a small town girl in the middle of Jesusland is not going to cave to the pressure to stay with the guy who crippled himself because of the "WWJD" social pressure involved? That shit happens ALL the time. She basically said in marriage counselling that she was not getting what she wanted (i.e. Dick) and Amv did not want to hear that at the time. And when she goes out looking for dong her first go to guy is the biggest asshole her husband doesn't like. The writing is on the wall for this one. Maybe too nice was the wrong word, though. Weak would be a better one.
Amer has to decide if he wants to live a life of distrust while making her miserable or moving on and (realistically) probably being alone for the long haul. It is not a happy thought, but its the reality of the situation. The lies are always what kills a relationship, more than the cheating. I am not saying this shit to be mean. If he drags her back into therapy or counselling again, then he is going to have to address the "not getting any dick" elephant in the room at some point. He is not interested in an open marriage, so that has to addressed one way or another. If they don't confront this (and the lying), then they are basically right back where they were with him miserable from a lack of trust and her sneaking around his back to get laid. Not a tenable situation for ANYONE, let alone someone with Amer's additional concerns.