I can provide some general insights that might help you understand why someone could be seemingly obsessed with an ex-partner, especially if that ex-partner had Borderline Personality Disorder (BPD). It's important to remember that every individual is unique, and their motivations may vary.
Idealization and Devaluation in BPD: People with BPD often experience intense emotional relationships, characterized by idealizing their partners initially. When the relationship ends, the person with BPD may struggle with the loss and continue to idealize their ex-partner, even if the relationship was tumultuous or unhealthy.
Unresolved Feelings: If the breakup was challenging or sudden, your boyfriend might have unresolved feelings or a sense of unfinished business with his ex-girlfriend. This could lead to thoughts or fantasies about getting back together.
Fear of Abandonment: Individuals with BPD often have a profound fear of abandonment. Your boyfriend's obsession with his ex-girlfriend might be linked to this fear, making it difficult for him to fully let go of the relationship.
Nostalgia and Positive Memories: People tend to remember positive aspects of past relationships more than negative ones. Your boyfriend might be focusing on the good times he had with his ex-girlfriend, leading to feelings of longing or nostalgia.
Codependency: If your boyfriend has codependent tendencies, he may feel a strong need to rescue or "fix" his ex-girlfriend, hoping to alleviate her struggles or make her happy.
Emotional Intensity: Relationships with someone who has BPD can be emotionally intense. Even after the breakup, the emotions and memories associated with that relationship might still have a powerful impact on your boyfriend.
Lack of Closure: If the relationship ended abruptly or without proper closure, your boyfriend might be left with lingering questions and feelings that he is trying to understand or resolve.
It's essential to communicate openly and honestly with your boyfriend about your feelings and concerns. If his obsession with his ex-partner is causing issues in your relationship, encourage him to seek support from a mental health professional. Professional therapy can help him explore and address his emotions, gain closure, and develop healthier coping mechanisms.
Remember that you cannot control your boyfriend's feelings or actions, but you can take care of yourself and set boundaries to protect your own well-being in the relationship.