I get it, I wanted my truth too. He's probably not going to give it to you though.
I don't know if this helps you in any way but here's what I did. I just accepted that absolutely everything I suspected and more was the truth. And when I let it hit me in the face I went into a deep anxiety attack that lasted a week and a bit. And when that was over, I was through playing nice. No more asking, no more hoping.
I sent her text after text after text telling her I knew exactly what was up and how she'd been cheating on me the whole time and playing me so I can watch her son for her. I called all kinds of 2-timing whore, I called her home wrecker a worthless parasite who couldn't get a family of her own, told her I hope she gets her cancer back. Just pure vomits of hate. She responded with her usual nonsense excuses and I shut them down for the liar she is. It felt reeeeeeeeaaaaaaall good and then it felt just as bad. From there on in, the tables were turned. I don't talk/text her unless ABSOLUTELY necessary and when she calls, it's her turn to be on the defensive while I treat her with all the inner a-hole I have in me.
It's not a constructive way to co parent, I know I'm being an @$$. The thing is though, I realize now that I was hurting so much for so long and it was my fault for being the nice guy. It's like I had to push way too hard in the other direction to balance things out.
I'm not recommending this way of acting. I do think though, you need to look at how you're acting and find out what you've been doing to give him power over you. Are you asking him to confirm what you already know full well? Are you keeping his secrets by keeping things unspoken? Are you letting him be the only one with weird sex toys and condoms that re-appear like magic? Are you letting him be the only one with the great social life you wish he didn't have? Do the opposite. Anything you were doing that put you in a victim position, do the opposite. In time you'll gain your own personal power from him.
I hope this helps provide some kind of insight.