Oh Juju...don't be so hard on yourself! I think we probably all go through something similar. I had similar issues with my XH. He had everyone snowed into thinking he was this totally decent, respectable, HONEST guy, but yet he cheated on me. No one would've ever believed me if I had told them that, so I didn't bother telling it other than in posts here and to a few select people in my life who I knew would believe me (namely, my family). Just like you said, you don't want him back, just think it is unfair. I felt exactly the same way, so I get it. I wouldn't take my XH back now if he were the actual last man on earth, but it still sometimes hurts to see him in a happy new "place" while I flounder in the cesspool that seems to be dating these days.
Your life is about you now. Take care of yourself, pamper yourself, focus on you and your beloved child and just rock your own world. You got this! Not to mention a new relationship who WANTS a relationship....awesome!
Me 52, H53 Bomb drop 9/29/2014 Divorce from XH final 12/17/2014 Marriage #2 12/31/2019 5 adult (step)daughters (3 from XH's first marriage, 2 from current H's previous relationships) 6 grandkids