It’s very easy to fall for the charm of a narcissist; and since charm often equals sexy, and sexy often equals sex, things get messy fast. Paradoxically, narcissists are often quite faithful in the early stages of relationships, because what frequently leads people to cheat is insecurity: If you’re afraid the person you love doesn’t love you back, you begin looking for your next landing spot. Narcissists can’t conceive that they’re not adored, so they don’t go through that phase.
But they’ll cheat soon enough, because for narcissists, a relationship is all about how the partner enhances their own self-image. That means always trading up to someone who’s younger, prettier, richer—or just plain newer. Narcissists will lie about where they’ve been and what they’re doing; they’ll listen less and less when you speak (not that they ever listened much to begin with), and they’ll leave you flat if you don’t leave first.