When I was younger I had a relationship with a married man that sounds similar; he confessed all to his wife several times and she forgave him and then he would beg me for another chance. He was a real piece of work and there was also an age gap and a power imbalance. Bad dude. The wife and I ended up talking right at the end and she really did seem prepared to forgive him everything despite the fact it was all ragingly awful and had gone on for a couple of years. Thankfully they had no kids, but they have stayed together.
My advice is to absolutely divorce yourself (ha! See what I did there?) from what he and she are doing. Block everywhere and be strict with yourself about this: it's better to know nothing. This was true for me for many, many years. Only now with a remove of more than a decade and a half and a whole new life can I even tolerate knowing the tiny amount I do. For a very long token it was too painful. You also have to be strict with yourself about having even an opinion about what they're doing... not your business. You do you, let them do them. If you've got a trusted friend you can get to help with this, all the better. The first year or so my fabulous tough-love pal was on this for me; checking I wasn't looking them up on Facebook or stalking his work's website to see if he was still in the same job etc. I needed that.
My second piece of advice ties into the first: get some therapy. You'll need a good therapist and regular sessions to stick to my first piece of advice anyway. They'll keep you accountable and help you work through your feelings as well as why you let this happen. I also felt like this guy was my best friend (and in lots of ways he was) and he left a gaping hole in my life, so therapy was invaluable. Funny, I also have OCD that, looking back, I've had all my life. Having that identified and treated came about because of my treatment via therapy after the affair. I was also diagnosed with ASD and ADHD (what we are now calling AuDHD, I believe) as a result of this therapy and, quite frankly, it explained a few things, including why I got into the affair in the first place. Such revelations may come to you in time, too.
Third piece of advice: keep busy. The devil makes work for idle hands, whether that be being tempting to contact/stalk your ex or his wife, or just obsess over them. So get some new hobbies, learn a new skill, do a qualification, join bloody line dancing... literally get involved in whatever is available to keep you busy and out of trouble. This also has the consequence of helping you meet new people and that's always good; new friends who don't have anything to do with that old life are a good thing. That said, don't rush into dating again too quickly. Getting caught on the rebound from something this big and ugly could be really unwise, so give yourself some time and space when it comes to a new relationship. Talk to your therapist about this.
Finally, be kind to yourself @TheMathofLoveTriangles. It's not the worst thing anyone's ever done. You aren't the first and you won't be the last. And fundamentally you deserve more in life than a cheating sack of shit can give you. You've genuinely dodged a bullet; however lovely you thought he was and whatever good qualities he had, he wasn't a decent person because a decent person wouldn't cheat on their spouse (and, even worse, keep going back to doing if after confessing and getting their wife'a forgiveness). You'll miss him, maybe for a long time to come, and that's allowed, but never forget the fact that he's not a good person and that you deserve to be loved completely, out in the open, and by somebody for whom you and you alone are enough.
Good luck, lovely. It's a hard road and a long one, but you can do this, you have the strength to do this. I promise.