I Have Borderline Personality Disorder

So, my best friend just got engaged a little bit ago. My abandonment issues hit me like never before. How are we going to be once she gets married? We barely see each other now. She's going to be in a family (fiance has 2 kids). I can't tell her how I feel. I'm ecstatic for her. She has been through a lot and deserves it. She deserved to be happy. I love her so much, but I'm terrified of losing her.