I've written those unsent letters---ripped up too many to count because I can't look at them again, like you mentioned, they bring so many things to the surface
I find doing a collage or other 'creative' work more helpful (then again, as I recall, splitting wood wasn't bad either...)
Or, something more structured. "moving on" begins to sound so vague to me...and not real (like "closure")---I think it is more about developing other interests and skills that take you away, moving into a different space with a different focus and feel.
Hope it works out well for you after all.