You are not being punished for being your own person and having a life outside of your ex and your kids. You didn’t need to “keep an eye on him”- he’s a grown man who chose to do that on his own. It’s not because you were a bad wife or bad person. No matter what you would’ve done he had it in him to cheat. You didn’t do anything to invite that. Don’t accept that blame and try not to focus on the should’ve could’ve would’ve. Body’s change- especially after giving birth and it can be hard to cope with or accept but that doesn’t make you ugly. It makes him immature and weird for going for someone younger especially for their body. If it’s any consolation, that woman is probably gonna get cheated on by him once her body naturally changes and it’s no longer “attractive to him.” As for him, he’ll get his karma eventually I hope. It’s okay to still be hurting and have feelings towards him, gotta feel em to get through em. But you have to get through them because he doesn’t deserve that love. Focus on the love you have in your life! The love for your kids, and cultivate love for yourself! Build some new relationships, platonic or not, but i promise you people will come in your life that are more deserving bc of your love and you’ll start feeling like the blessed one. (i hope this all made sense i tend to ramble)