How do I take control back from a sociopath?

I have struggled for the last 4 years with a narcissistic sociopath that dates my partners best friend. It’s like everything I do, she does and even though I don’t often see her, I’ve been ruminating constantly over everything. She’s turned most people I know against me and always plays the victim which has caused issues between my partner and I and his friend. I found strength in it all last year but after she wiggled her way into another area of my life recently it’s all come back. A friend referred to our situation as emotional abuse and I’m exhausted. How can I get her out of my head once and for all and not have her affect me the way she does? I’m notmally a very confident person who doesn’t let anyone get to me, except for her.