People with NPD - and people who are simply on the high end of the narcissistic spectrum - can come across as charming at first. This can make it easy for them to get into relationships or land jobs.
But people with NPD have difficulty maintaining healthy relationships over time. Some of the same traits that may have helped at the beginning of a relationship can rub people the wrong way over time. And that's just the tip of the iceberg. Narcissists can exhibit all of the classic abuser behaviors, such as being strictly controlling and seeking to isolate their partners.
Ultimately, being in a relationship with a narcissist can range from exhausting to damaging, and you need to look out for yourself because they aren't going to do it for you.