My mum left when I was 12, with my Dads best friend with whom she'd been having an affair for 3 years.
Over and over in my life I've ended up getting depressed and having therapy for the current "obvious" reason, it took a wonderfully thoughtful and caring psychiatrist when I had pnd with my 3 rd child to pin it all together for me. I was still going back to being a child and feeling that hurt all over again (she said some very difficult things to me when I saw her again a month later). Everything that happened triggered it.
I worked really really hard on myself after that. I got over my drinking problem, went back to education, brought up my 3 now young adult children, worked on my marriage (to the extent we're quite looking forward to being empty nesters in a few years!). And now, 17 years later I'm training to be a psychotherapist myself!
I also cut ties with my mother 16 years ago. It was not, and never was going to be a healthy relationship, and she continued to let me down. She's now old, sick, and not my problem. And could be reading this now if I have read things correctly. I don't care.
I'll never be over it. There's always going to be that 12 year old weegie in there, but I've learned to look after her and soothe her, and live my life as an adult in a healthy, life-giving way.