I had a friendship for a long time that I cut off in Jan 2020. We were friends from 17 and we went through a lot together.
I still miss her even now but she's not good for me.
It wasn't a man but everytime she got a new friend, I got dropped and then whenever it went wrong, as it inevitably did, she would run back to me.
She had her own problems, told lots of lies about herself so it didn't bother me as I knew it was self esteem issues and everyone else was the problem, never her. However, she was also fiercely loyal and when I needed her she had my back. And because she had been through so much, she got away with it far longer than anyone else would because I always made excuses for her. She was manipulative when she wanted to be.
The last straw was when I didn't hear from her for several months. Despite me sending messages. I could see she was reading them but not responding. I left it for a month then I sent a message asking what was going on as she'd done this before when she had some issues. She did the same thing. So I blew up, called her a shit friend and blocked her. I'd never said this to her before but she hurt me.
She then after, kept using her daughter as an excuse to try to talk to me (text me from her phone) saying I know you don't want to talk to me x2 but my daughter was worried about you over covid and wanted to keep in touch with me.
It was hard for me because I was close to her daughter but I had decided to let it all go for a clean break. This was her typical behaviour towards me, trying to manipulate me and make me feel sorry for her again. She was never sorry but that was her way. And this time I didn't fall for it.
I've had to let go of a few friends that weren't good for me or my self-esteem over last few years but that one hurt, because like you she was a sister to me.
However, we shouldn't tolerate bad behaviour from someone who supposedly cares about us. Once is a mistake but over and over? Then that's on us. Just because they are a long friend, doesn't make them a good friend and that's what I remind myself every time I think of her.
She'll never change. If she did, I'd be friends tomorrow but she won't and I'd be kidding myself. I can breathe now without these people in my life. I hope it gets better for you.