Clinging to past anger and pain is very easy, but usually very destructive as well. If I wanted to buy a horse, and I saw one was "Parelli-trained", I'd ignore the ad and keep looking. But in fairness, there have been people on HF who have had positive experiences, or learned something from a licensed Parelli trainer that helped them & their horse.
As a suggestion, take some long rides (or a lot of short ones) and think about what you learned, both about horses and people, and both to the good and to the bad. Maybe write them down, to help you keep track. Then move on. Use what you learned to make tomorrow better...but move on.