Instead of constantly complimenting and praising him, you need to focus on his flaws and imperfections. But for you to do this, you need to take off your rose-tinted glasses and see this guy for who he really is and that will help you see that he is far from perfect. Once you achieve this, you need to make sure to constantly imply his flaws to him.
You don’t need to insult him directly. Instead, give him doubt about his physical appearance or about his brain. This is the biggest punishment for a narcissist. He will never stop feeling insecure, the way he wanted to make you feel, and he will start to question his every move because he has an uncontrollable urge to be perfect in everyone’s eyes and especially in the eyes of his current victim. Therefore, this guy will do everything in his power to get your approval and to regain your admiration because that is what feeds him spiritually.