Past relationships are in the past for a reason. Some end up there because of indifference, some end up there because of miscommunication, some end up there because of the consequences of malice, and others end up there simply because one human being took a path different from another. But no matter the reason, what most past relationships have in common is this; they should stay there.
It’s similar to the best experiences of our lives, those days which we feel are without comparison. By trying to recreate and re-live them, we pollute them. Attempts to re-capture those days, whilst born from a sincere nostalgia, often result in the compromising of their very memory. We go to places that are special again and again, and thus they stop seeming so special. We try and try to re-establish old contacts, and in the process replace fond memories of the time spent with that person with bitter resentment at their refusal to re-engage with us.
The past is dead. We cannot bring it back to life. All we can do is appreciate it, cherish it, say thank you for having experienced it, and then switch our focus to the present and the future, to the creation of new experiences and new relationships that will also, eventually, become a part of our past.