I used to have horrible, horrible memory thoughts plague me constantly. They were of the bullying I went through. I would relive it over and over again. I couldn't sleep because of them. I would actually like lash out physically at the thoughts, shaking and batting the air. Years and years after things were over I was still thinking of "what I should have done/said" instead of what really happened.
Then, one day, I felt safe for some reason and I released them. I still have the memories but they are faded and far away. I don't know. I just suddenly felt safe and loved and they went kind of by themselves, but I was able to let them go.
So my advice is you have to feel safe, and then it's easier to let go of the bad thoughts.
Another example of this is that during the bad time, I built up a lot of these thoughts about what was happening. They kept clinging to me and I kept talking to my husband about them. Even arguing with him about it when necessary. These discussions and arguments were necessary in healing, I think. Little by little, they are letting go of me and I am letting go of them. Because I'm re-discovering safe. If that can't be done, it can destroy everything.