"All of last year (and before I met him) i wanted to get back in touch with the version of me that existed before my marriage and pregnancy, because I was happy then and not bitter like I am now. Then I meet him and he's everything I wanted back then and reminds me of everything I was back then, he makes me feel like I'm 23 again."
Back then you wanted a man that sleeps in bed with another woman every night? Who cuddles up with his family for movie night, shooting you the odd text to keep you sweet? Possibly showers with another woman, holds her hand in the cinema etc.
"I sometimes see him as an obstacle to my own happiness, but I haven't nuked the whole thing because I know I deserve to give it a chance (despicable behaviour aside)"
His behaviour isn't deserving of anything except contempt? He's stringing two women along, one of whom seems to be having mental health issues, (which would make you vulnerable to creeps like this).
You can be happy, you can be the best version of you possible. You can reclaim some of who you were at 23. You can reconnect with your dd, and learn some empathy. You could be a catch. But not while you're fucking a family man. Plus, talking from experience, some men who cheat have a nasty side, that their fuck buddies don't see. That's reserved for the mug at home, who does their laundry, cooks for them, does the brunt of childcare, and can't work out why he's suddenly so on edge, defensive, secretive etc. If he leaves her for you, I fear he'd end up treating you the same way.