We had been somewhat close friends for 4 years, and had initially started talking with the intention of dating although things did not work out since we were so young. Ever since I've known her, she has displayed narcissistic tendencies and I have had the general feeling that something was different in the way she thought about herself and others. Eventually, we both left our previous relationships to be with each other. 

Everything was beautiful. Pure bliss. Every single moment. Then it was time for me to leave for university. It was as if a switch flipped. Without me being there, she began to behave like I did not exist. She began being promiscuous with other men, posting pics of them and very revealing pics of herself. This lead me to believe she was a narcissist. But as time progressed, I realized that she genuinely did think of me as 'the one' and would fight so hard anytime I threatened to leave due to a crossed boundary.  

It became an exhausting push and pull on my mental state. I would become physically ill, and neglected my priorities and health to an extreme extent. The worst part was that she knew what she was doing was wrong. She would say, 'I know I can control my behavior, its not as hard as you seem to think' So I kept giving her chances. She would scream at me and cry and come to my house and spam call me any time I tried to leave. She claimed to want to change for me. This is when I figured that this is probably not narcissism and most likely BPD although I obviously cant say 100% (not like its black and white either).

She was amazing, and if BPD was not a thing, I probably would have married her. But I think that I am too vulnerable in my life right now to sacrifice my mental health for hers. I know she is struggling very hard without me there, no matter how hard she tries to hide it. I know what happens when I leave because she has shown me videos of her becoming hysterical and crying and slamming her face on her pillow and other stuff. At first I was angry, jealous, and felt betrayed. But now, I just feel genuinely sad for her. She lost me and I know how badly she needed me. I doubt she will be able to build any healthy relationships in her near future. She always expressed a desire for therapy but her parents would not allow for it as it damaged the family appearance (crazy narc behavior). I wish I was able to stick it out.

 Should I have kept trying, for the both of us?