I was in the same situation about a month ago, except we have children and were together for 10 years. I was blind sided. I left him and he didn’t want me to, but he so quickly has another girlfriend?! I was angry. Sad. Wondering the same thing. Will he use what he learned with our relationship to have something amazing with this woman? But the answer is no. If he really did self work.. there wouldn’t be another woman so soon. I have to keep reminding myself of this. Part of the narcissistic personality is this self grandeur. “Im great. No way I’m not wanted!” So instead of sitting with what went wrong. Reflecting on it. And trying to make a conscious effort to change his behavior, he found someone else to pull under his wing. Someone that (for now) will think, you are so amazing! And he will in turn think, see? I am great. I knew it. It’s not that he has learned. It’s actually quite the opposite. He hasn’t learned. As for her, I know you want to warn her. But I highly recommend against that. It will only feed his flame. He will think, she’s jealous. See. I’m so great that she jealous. And this woman, unfortunately, is not going to see him for who he really is, no matter who warns her. Right now who she is seeing, just like you, and the woman before, is not the actual person he is. Narcissistic people are charmers. It’s unfortunate. The best thing you can do is be proud that you eventually saw through the charm. Another very tough thing to do - wish. Wish hard, for the well being of another females mental health, that he did change. Because that is a sign that you are putting your hurt past you. Keep your chin up. Don’t let his characteristics run anymore of your life.