For me, sometimes it's hard to tell when I am digging productively versus when I am ruminating, which is (particularly for females, according to Martin Seligman) a major source of depression.
I think I can only stop the endless recycling of my NM pain (which is NOT to say that the pain didn't have to come out, it did, and it took years)...but I think I can only stop it when I really really understand that NM was, however selfish (and she was less cruel than others here) ... a damaged human being who had been cheated of the authentic happiness a whole or healing person can achieve.
Ultimately, she was witholding nothing I could not learn, with spiritual and community help, to build for myself and those I love.
So ultimately, it was seeing her humanity and forgiving her (not forgetting), that released me to stop the recycling.
Bluntly, it was also her death. But even before that, I was learning to no longer suffer over her inability to love.
xo
Hops