“Their superficial approach to relationships means that it is very easy for them to replace people (including their partners) and find someone new rather quickly.” – Ramani Durvasula, Ph.D.
So if you see them with someone else quickly, keep in mind that they’re probably “love bombing” them in an effort to use them. Be glad it isn’t you anymore.
Furthermore, according to Ramani Durvasula, Ph.D. in Psychology Today, it’s a bad idea to assume that “someone else is going to get the good version of them”.
She says that the “better version” does not really exist. The way that you were treated is exactly the way that their new lover will be treated.
Narcissists tend to be pretty stable in the way they act in relationships.