Why can't i feel like myself after my husband's affair?

i've been trying so hard to feel like myself again since my husband admitted he had an affair with a 22-year-old while i was pregnant and after i gave birth. i thought i was making progress but some days it feels impossible. we've been together for 13 years and married for 4. now i look at him and feel like i don't even know who he is.
this isn't the first time cheating has shattered me. when i was a teenager an ex cheated on me with a younger girl who even had the same first and middle name as me. i was young and completely fell apart. i smoked drank used substances and couldn't afford any mental health support. i even confronted the other woman because i was convinced she had something i didn't. eventually i realized i wasn't even fighting for him. i was fighting the feeling that there had to be something wrong with me.
then i met my husband. i truly believed he was the person who helped me heal from all of that.
now it feels like i've been broken all over again. almost like he helped put the pieces back together just so they'd fall apart once more. my self-worth is at its lowest. i barely recognize the person i see in the mirror and i struggle to find any sense of purpose. if it weren't for my baby i'm scared to think about how far i might have spiraled.
how do i start believing in myself again? how do i stop feeling like someone else's choices define my worth?