Tips on recovering from 6 years dealing with a narcissist please

My partner's ex-wife is a narcissist. I've had people on Reddit suggest that my partner is a narcissist but that's definitely not the case. We all know how a narcissist weaponises people. He's never told me he was weaponised, he still can't face what happened. He's very gentle but not as strong as I needed him to be to get through what she did. He had been in an abusive relationship with her for 15 years and she was using the kids and through them him to get to me. I assume I threatened her idea of herself as utterly central to the kids' worlds and when her daughter showed any enthusiasm for me it all exploded. She turned her against me, everything I said or did was extracted from his daughter and twisted and then both of them were telling my partner I was the reason she didn't want to come over. She'd send long essays about how she was the only one who cared about this child she was hurting. He had no idea what to do for the best and was afraid of losing his kids, because she would have made that happen. My stepdaughter who'd been the scapegoat her whole life up to that point was suddenly the golden child and I became the scapegoat. A woman she'd never even met. She'd tell anyone who'd listen how terrible I was. I'm autistic and very straightforward, so the confusion and injustice of it eventually brought me to the point of burnout and I ended up in counselling and eventually leaving. She instantly lost interest in me, and 3 months later in her daughter as well. She'll have forgotten all about it, but I can't get over it. I'm anxious and depressed and still have nightmares if she causes any issues for my partner. I decided not to have any contact with my stepdaughter because it caused all this trouble me being in her life, and because I would get on edge if I saw her. I know she's had so many more years of her behaviour than me and it was hard to concede I couldn't help her.

I was there for 6 years and left 10 months ago. I don't want the kids to know where I live in case it gets back to this woman. I don't want to see the kids in case it sets her off again. It took my partner and I 6 months to be able to talk about it. It nearly destroyed us. His daughter is starting to tell him now what I told him all along, that her mum was intent on being the only person in her life, whatever that took. I'm sure it was easier to believe I was the problem, I'm sure I didn't help in some ways and found it difficult sharing a house where his ex dictated how things went, down to her telling me through him that I should be OK with the kids going through my possessions and using or taking whatever they liked. I ended up not sure whether I was actually the bad guy. You know how it is. It was like she was in the house with us.

I live alone now and I'm not sure how long it's going to take me to get back to calm, let alone happiness.