When you break up with a Narcissist and they find out (yes they will keep tabs on you) that you have started dating someone else, often times the Narcissist will come running back to you. You were once their Source of Narcissistic Supply. Yes, they have a new Source of Narcissistic Supply, but the Narcissist fears losing you as a fallback option of Narcissistic Supply, when you start dating other people.
Talk to those who have broken up with a Narcissist and they will tell you that its never a good idea to fall for the empty promises of the Narcissist.
Video is courtesy of the Lisa A. Romano Breakthrough Life Coach YouTube channel