Processing Grief

I’m trying to process the grief of the loss of a relationship- that I’m choosing to end. I feel that I have not permanently ended it despite trying for several years because I have never processed the pain and grief of the loss and end up letting the person back in my life. I want to stop the cycle and be done. I find myself sad and angry and I’m trying to distinguish between indulging in that feeling vs. feeling it, not resisting it, and processing it.
What should I be doing when I’m just allowing the feeling? I know my thoughts are creating the feeling so I know I don’t have to feel this so I just want to jump to feeling better. How do I know when I’ve significantly allowed the feeling?