I'm so sorry you're going through this, but you will get support, info and advice from this site. I hope it helps.
I don't know if I'm going to say anything original but maybe just confirm what others have said or will say:
THIS IS NOT YOUR FAULT. THIS IS ENTIRELY 100% HER FAULT, IT IS ALL ON HER. THERE IS NO EXCUSE FOR CHEATING. NONE, PERIOD, EVER, WORLD WITHOUT END AMEN. DO NOT ACCEPT ANY BLAME FOR THIS, DO NOT LET HER PUT IT ON YOU.
I mean every word of that. Could your marriage be better - yeah, all of our marriages could be better. Everyone's could be, everywhere on earth. But there is no excuse for breaking your vows, lying to your spouse, taking up with another person, giving him or her the attention and affection and sex, because, yes SEX IS IMPORTANT AND IT DOES MATTER. That exclusivity DOES matter to most people. It's the reason why the Bible allows only adultery as a reason for divorce....because the physical bond IS the marital bond and having sex outside the marriage, breaks that inherently. Not to say that emotional affairs don't cause problems, they do, but when it goes to physical....something fundamental has broken.
I'm saying all this to validate you because it sounds like your wife is trying to project onto you and blame you for her actions and DELIBERATE DECISIONS - every time she made any move or response to this guy, it was a deliberate decision, NOT a mistake, and she has to own up to it and not blame you. DO NOT ACCEPT ANY BLAME AT ALL. If you do, she'll just use it to deflect her own responsibility and blame you. She's trying to escape blame, responsibility and consequences. Don't let her.
There's probably more that you don't know about. I don't know how you can find out at this point, unfortunately it sounds like she destroyed much of the evidence which is what cheaters try to do. You might get some info from going through phone bills - the numbers and frequency of calls and texts should be available and sometimes even text messages depending on carrier. If you can get into her phone - and always do these things secretly and NO YOU DO NOT NEED PERMISSION - there is no secrecy in marriage (or it's not a marriage....two become one or should try at least)....and look for apps she might use to cheat, or deleted files. Sometimes these can be recovered. It might not be a bad idea for her phone to go missing for a couple of days if you get my drift. Also, check Facebook and other social media platforms, and check credit card and financial records. DO NOT ASK PERMISSION DO THIS SECRETLY. Your wife has acted in secret, unfortunately affairs set up spouses as ADVERSARIES because she has taken secret action against you, even in undermining you to her friends. Something that also commonly happens in affairs because she's trying to give herself reasons for cheating. Trying to feed the dissatisfaction.
I think the biggest ongoing issue with adultery is that it totally changes how you view your spouse. Someone you think you knew and could trust and predict their behavior, maybe for decades, does something you could never imagine or foresee. You see a whole different side of them and you wonder....who is this person? Not only how could he or she do this, but WHO IS THIS PERSON? It can make people call into question everything about their marriage and certainly.....how well you know your spouse and if she was like this all along. Who knows? So it's not only that TRUST has been broken but....IDENTITY has been broken too. You don't know who you're married to now, who you have been married to, and what she is capable of. I think that's a big unacknowledged part of what makes this so frightening and disorienting....as well as angering. Our whole basis for a secure life based on a partnership with a known person has been thrown up into the air and become a Twilight Zone episode. Don't underestimate these feelings in yourself. This is, IMO, ultimately what makes reconciliation so hard if not impossible for most people (I don't generally believe in recon myself)....it's not only the basic issues of understanding why she would do this, and whether she could ever be happy with you or will keep finding others (or with this AP), but.....WHO IS THIS PERSON? HOW CAN I TRUST HER AGAIN? HOW CAN I EVER KNOW WHAT SHE TELLS ME IS TRUE AGAIN - including whether she loves me? Maybe that's just another big lie of convenience.
To become vulnerable with someone on such an intimate level over a period of time....requires great trust and belief they won't betray us, lie about us, steal from us, have sex and love with someone else....and once that is broken, people can try to get it back. They call it spackling when you pretend everything is as it was because you drive it beneath the surface, but the feelings and distrust don't go away for many, nor should they necessarily. You don't know this person anymore, maybe you never did. How you can build up that sense of trust, if it is possible again, is an individual thing, but DON'T PUSH YOURSELF FOR IT. Staying together for the kids or money or health issues is fine as long as you acknowledge that's what it is. But don't pretend you feel or don't feel things you don't. And don't accept DISRESPECT FROM ANYONE, PERIOD.
If this were me, and I did not have kids, financial issues, etc, I would probably file for divorce now. It might be the only way you're gonna get the truth out of her. It tends to WAKE PEOPLE UP. And it is usually the right thing to do. She BROKE the marriage, if you do stay together eventually, other than for the kids or money, it would have to become a new marriage based on a new understanding of who she is. And how she views you and what she wants from the marriage. You have to be able to believe in that.
I would go to a divorce lawyer, see what divorce looks like for you and be prepared to file. Even if you don't, you will have the knowledge and you need that. You don't know what's going on with her and I've seen women just up and leave. Don't be a chump, check it out for yourself. And get an STD test. And don't bend over backwards kissing her ass. To me, cheating is damn near unforgivable....some might be willing to....but don't make it easy. The easier you make it, the less respect you will get and I think LACK OF RESPECT IS A BASIC FACTOR IN CHEATING.
Good luck, Worried! Investigate secretly, get info, be bold, take action. As a woman, I will tell you, I like men who take action and are assertive. I think most women do. Keep that in mind.