A narcissist is basically an empty husk of a human being who manufactures an attractive exterior in which to fool the people around him or her. Narcissists do not know how to feel love, pain, empathy or guilt, and seemingly surround themselves with people who have the exact qualities they lack.
A narcissist cannot continue putting up their mask to the world on their own forever. They need constant reminders of what it is really like to function as a normal human being. So they look for these types of people and emotionally entangle themselves with them.