Not true. People communicate far more effectively at the beginning of a relationship. At the end, often communication breaks down to a considerable degree or is characterised by statements of anger or hurt that can display very little of someone's essential personality. People undergoing huge stress seldom communicate well.
A narcissist paints a picture of themselves as being the victim or innocent in all aspects. They will be offended by the truth. But what is done in the dark will come to light. After all, time has a mind of its own!