I was diagnosed with BPD a few years ago, and I guess I never really thought too much about how much I struggle with romantic relationships. I’ve had a lot of relationships with people. Flings and such, but I did have one girl I did love. I met her in high school and we ended up dating my junior year. We dated on and off for a couple years, until it completely ended after she cheated on me with a married man. It broke me, but I know I shouldn’t have been in a relationship that was on and off anyways. It’s been a little over a year, and I am happy to say that I’m over it. We are friends now, but I still think I’m overly attached. We talk everyday still. I don’t think of her as anything but a friend, but I’m afraid to let her go. 
With this being said, recently, I met someone. She was really sweet and filled my head with bullshit about actually liking me and stuff. It made me feel special but now she doesn’t want me anymore because she “doesn’t want to get hurt by getting attached to me”. I’ve only known her for a month, but she has been the first person I’ve developed feelings for since my ex. I’m not sure if I’m overly nice, or maybe I’m too weird. (I’m a huge nerd. I attend science seminars and stuff like that). But, I will say I never said anything like “I love you”. I took it very slow. What changed it all though was when I said, “I hope that we can spend more time together.” And she just went off and told me that she wants that but she doesn’t want to get attached. Everything was fine, and then she started to go see an “old friend” and then stood me up and doesn’t talk to me as much. I’m trying to not take it personally because I understand how hard it can be to let go of someone that you love. 
Anyways, it still hurts to know I’m not wanted. But now, I just think I have a problem though, because I really put her up onto a pedestal and put a lot of hope into a healthy relationship. I did this with my ex as well. I honestly believe these people will fill this void inside myself. Why do I only find happiness in how others make me feel? I mean, I do have things in my life that make life fulfilling, and I’ve worked so hard to be mindful of my toxic behaviors. It just never seems to be enough for me. My goals and the things I accomplish don’t bring me any joy anymore. So, I guess my main questions are:

How do I make myself content with being alone? 

Why do I need everyone else to validate that I am wanted?

How do I fill this void inside of myself?

Why can’t I let go of the people I had romantic interest in?

(I am asking for advice, not because I want strangers to tell me that everything is going to be okay or because I need validation. I am asking, because I am struggling to fix my own flaws. I am very lost and scared within myself. I’m so very tired of being bitter and sad. I want to be a better person.)