I've heard the stories from women who vowed to save their marriage and shake their husband back to sanity. Frankly, I couldn't do it. Though there's little doubt in my mind that a whole lotta these guys completely lose their minds in the midst of an affair, I don't think it's up to the betrayed wife to try and convince them to smarten up.
The way I see it, you likely don't have the energy or the motivation to bring him back from Crazyville. He hopped that train and it's up to him to find his way back.
Your only job is to figure out whether you want him back once he arrives. And most of them will arrive. Most of these guys weren't looking for a way out of their marriage...just out of their doldrums. Or their emotional isolation. Or their crappy childhoods. But that's for them to sort through with a good therapist.
Your simple task (beyond hauling your betrayed butt out of bed every morning and attempting to get through your day) is to really think about whether he's worth giving another chance. Some of 'em are. Plenty aren't.
How do you know? Well...you give him some tests, kinda like multiple choice, except there are no "guesses". This isn't about anger or revenge or "an eye for an eye." It's about treating yourself with respect...and demanding the same from him. Whether he can answer these things right away or he needs to sift through his own confusion doesn't necessarily indicate whether he's a good guy who screwed up or a total scumbag. Some of these guys have this ass backward. They figure that, 'if I had an affair, I must be unhappy with my wife'. When the truth is, they had an affair because they're unhappy with themselves. But it's so much more convenient to blame someone else. And it can take time to come to that unpleasant but ultimately true conclusion.
Choice #1: Does he want his marriage or doesn't he? If he picks yes, then he's got some homework. Starting with a No Contact letter to his OW. No emotional good-byes. No "just one more meeting to let her down easy." No, "but she didn't know I was married. She got hurt, too." Simple, straightforward and vetted by you. Along the lines of "I made a terrible mistake getting involved with you and I've chosen to try and save my marriage. I will no longer have any contact with you. I insist that you respect his." You could ask that he threaten legal action if she violates this, but that might be unnecessarily inflammatory. Depends on just how stalkerish his OW is. His loyalty needs to be to you, right now. Your feelings are the ones that trump anyone else's.
Choice #2: Is he willing to accept responsibility for the pain and betrayal he's caused you. That's not to say responsibility for the fact that your marriage likely had its issues. But total responsibility for lying, deceiving you and potentially risking your physical health. If so...good. But he still needs to work with a counsellor to uncover why he made this choice...and put boundaries into place to ensure it doesn't happen again.
If not? Well...don't let the door hit you on the ass on your way out, buddy.
Choice #3: Is he willing to offer complete transparency in order to regain your trust: access to any and all e-mail accounts, texts, cell phones, computer passwords, credit card bills and so on. Trust is tough to earn...and easy to lose. It's going to take time and steady proof that he's being honest with you. "Trust...but verify" is your new motto.
Choice #4: Is he willing to do whatever it takes to be the man you thought he was (assuming you thought he was a decent, loving husband. If you thought he was a total jerk even pre-D-Day, then your marriage has more issues than infidelity). This means answering your questions even if you've asked them a dozen times, holding you while you cry, listening while you scream...and supporting you through likely the most painful experience of your life.
Then – and only then – does he deserve his second chance.