In terms of letting go of what someone has done to us, I think that's a process too. I've found that along with distancing myself from the individual, living my life in a positive & healthy way helps - living in the moment, experiencing joy more often (I really like to laugh, for instance) - like intentionally putting myself in joy's way..helps with letting go.

Honestly, I don't have the psychological part of it down, like stuff still pops up for me, but its something I'm working on. Maybe "telling a different story" about the past situation could help. Reframing. As long as its true and not a lie, imo. If I'm ruminating, giving myself a 30 min time frame (example time) to think about it (or focus on a solution) in a day and then move on, helps.