The correct answer isn't to let go of your past but to accept it and recognize for it what it was without holding burdens from it. Learn from it but do not necessarily let it determine who you are now. You speak to ex's only if you can recognize the feelings which may arise and be at terms with them. Most people can't do this and usually associate certain reactions and feelings with the person and thus still dwell on what it was. Thus, it is usually healther for them to stop contact with them but that doesn't mean the internal feelings about them are removed, it just means the trigger for them has disappeared. Anyways, the answer can be much more complex.