I know and I had cut ties with her for months until one day she messaged me on FB wanting to talk because she was upset as her dad caught Covid and was hospitalised for well over two weeks. I thought ok, i'll give her a shoulder to cry on, on messenger. After her father came out of hospital she then got a little closer and wanted to go shopping etc. It'd be fine for a few days then she'd blow cold again and say that we shouldn't be so close etc. Then her mind would change again, usually when she wanted me in the bedroom. I'm not interested in that and i'm upfront about that and I will tell her again. I'm not wanting to be controlled or want her to think she has any over me, she very much doesn't.
I know exactly what she is doing. I'm basically the safe bet for her both emotionally and sexually, that is until she meets someone else. She certainly doesn't like me meeting any other girl(s) and has told me this, even bringing it up a good few times in conversation but in a jokey way (not really jokey). I really do think that she wants me to be jealous about her and her meeting other people. I'm just not and I know it irritates her. Like this for instance... (I find this odd and no idea how this works). She says and has shown me all these friend requests that she has got on Facebook from fellers, most, if not all are foreign. I've no idea what she's been doing as that doesn't just happen. But again i'm not bothered by it, but I know she's trying in a way to get a reaction(?) from me.
Ignore, block, and move on. By maintaining contact (no matter who initiated it) you're playing her games and giving her the attention she wants. She'd be thrilled to know you've come here to tell the tale. The fact that you don't cut her off shows her that you just can't live without her, and she can continue to mess you about to keep you on the back burner. No matter what you say, your actions speak otherwise to her.
If you meet someone else and get a new girlfriend, you're just storing up trouble for yourself because you've let your ex believe she's still part of your life and has first dibs on your attention.
As Steampunk says above "Ignore, block, and move on."
I feel she sees you as a resource to be used to fulfil her emotional and physical needs when it suits her, and that is what you are allowing her to do.
This will only stop when you stop it.