What should you do if you notice your partner is acting narcissistic?

Suggest going to therapy if you'd like to try salvaging the relationship—just keep in mind that many narcissists dislike therapy, as it forces them to be accountable. You could also try to communicate with them about their behavior and the way it makes you feel. However, if they aren't willing to cooperate, the best thing to do is leave. Narcissists do not change and will continue to be difficult people to be in a relationship with. You may also benefit from going to therapy on your own (without them), because dealing with a narcissist can be very damaging internally. It's also important to find a good friend (or friends) to vent to because you'll definitely need someone validating to talk to who will help you realize that you aren't crazy.