My ex didn't admit for years. There were 2 ow in a short space of time.
Wee mcbeastie I don't agree people don't cheat without a reason. There's excuses not reasons if the relationship is making you unhappy you talk to your partner to try and resolve or you leave.
However we also had similar experiences my ex had been distant for some time and we'd already had a separation the previous year and got back together. During a row he got in my face and spat at me that he was gonna end the marriage but was gonna make it look like my fault so everyone would hate me and blame me.
But he wasn't clever enough because there was evidence (he wasn't even bright enough to put a lock on phone let alone delete texts, nor change the password to his email, he's even on video kissing his now wife when we were still married. Also she announced pregnancy very soon after I kicked him out once I felt I had enough proof).
Revenge - living well without him - sounds trite but you know what? Even when things have been shit for me I have NEVER let on to ex. As far as he's concerned I'm happy, and doing just fine without him (and when things are shit it's nothing to do with not being with him or our split and honestly if I were still with him I think he'd make things worse).
Meanwhile he seems to regularly forget I still hear exactly what's going on with him and it is NOT all roses by any means.
He's cheated on wife 2 regularly, has 5 kids he didn't want, is unemployed because he fucked up at work (affair has contributed to this), is not ALLOWED a mobile phone or social media accounts because of his cheating, she's installed spyware on their computer.
She's not happy either as she's having to support him and apparently he does bugger all at home. You reap what you sow.
And she did know us and knew we were married and had a child.
Not every ow knows (but I think is very rare and only in certain circumstances, I think many don't want to know or don't care) but both 'mine' did (one was supposedly a friend!)
You WILL get through this, you WILL see that you deserve better and that they deserve each other. Sleep when you can eat what and when you can, drink plenty (not alcohol) and do things that distract/make you happy. 