Word for feeling of closure or peace of a relationship (usually a bad one)
Perhaps, catharsis — M-W
2b : a purification or purgation that brings about spiritual renewal or release from tension
"She has learned to have her catharsis, take a deep breath and move on. … she does not dwell on the negative anymore." —Selena Roberts, New York Times, 24 June 2001
Wikipedia explains in detail:
Stages of social catharsis:
Directly after emotional effects, the emotions are shared. Through sharing, there is a reciprocal stimulation of emotions and emotional communion.
This leads to social effects like social integration and strengthening of beliefs.
Finally, individuals experience a renewed trust in life, strength, and self-confidence
There are two possible words which can be used in such scenarios-
1.Detachment
2.Equanimity - is a state of psychological stability and composure which is undisturbed by experience of or exposure to emotions, pain, or other phenomena that may cause others to lose the balance of their mind.
There is one more beautiful word synonymous to peace- Serenity, which is perfect for such situations.