Staying as friends with your ex-partner is a matter of personal choice. However, psychologists say that there is a specific reason why someone likes to keep in touch with an ex-partner. This is done mostly by narcissistic people.
Some people, after the pain and frustration stop, they will realize that they still have a tremendous platonic affection for their ex. Or simply recognize that they function better as friends than as a married couple or partner.
Others, however, do not want or simply cannot find a way to change the nature of the relationship to keep a particular person in their life. But narcissists often have a habit of staying in touch with their ex just out of necessity.
Several factors are subject to this behavior. Narcissists often struggle with the fact that someone has abandoned them, and they also struggle with inherent insecurity.
Narcissistic people are prone to that primitive feeling of abandonment, especially if the person they were once in a relationship with is rich, powerful, attractive, much younger than them.
And finally, narcissists love to have secrets because secrets are a sign to them that they have power. That doesn’t mean you will believe that everyone who stays in touch with his/her ex must be a narcissist. Sometimes business or job can reconnect them but without affection or intimate feelings.