It's challenging to provide a specific answer without knowing the individuals involved and their unique circumstances. However, there could be several reasons why your narcissistic ex's new girlfriend might be obsessed with you, even though you don't want him:
Jealousy: She might perceive you as a threat or competition, especially if your ex still maintains some level of interest or connection with you. Jealousy can drive individuals to obsess over someone they perceive as a rival.
Validation and Comparison: In some cases, people seek validation by comparing themselves to others. If she feels insecure about her relationship or herself, she might obsess over you to boost her self-esteem by convincing herself that she is better than you in some way.
Idealization of You: Sometimes, individuals in new relationships might idealize their partner's ex, especially if they perceive the ex as the one who got away or the one their partner might still have feelings for. This idealization can lead to an unhealthy obsession.
Narcissistic Traits: If she shares similar narcissistic traits with your ex, she might view you as a threat to her self-image and feel compelled to undermine you or prove herself superior.
Lack of Closure: If your ex's new girlfriend knows about your history with him, she might be seeking answers or closure about your past relationship.
Unhealthy Relationship Dynamics: It's possible that the new girlfriend is being manipulated or controlled by your ex, leading her to become obsessed with you or to act on his behalf.
Personal Insecurities: Her obsession with you might stem from her own insecurities, fears, or unresolved issues that she projects onto you.
It's essential to remember that you cannot control how others feel or behave, but you can take steps to protect your well-being and boundaries. If her behavior becomes harassing, threatening, or negatively affects your life, it may be necessary to involve authorities or seek professional advice on how to handle the situation.
In any case, it is crucial to prioritize your own emotional well-being and focus on building a fulfilling life that does not revolve around your past relationship with your ex. Surround yourself with supportive friends, family, or seek help from a therapist to process any lingering emotions or concerns.