I've heard people with BPD described as the great outsiders. Actually, it was by Dr. Linehan herself in a documentary on BPD that I saw recently.

I've felt this exact same way more times than I can count. I've lost most of my friends, haven't had a significant other in years, and my family has abandoned me because they have no idea how to deal with my illness and shy away from mental illness. Usually, I am able to accept my life reasonably well; this is what I have and I need to be happy with it. When I get around normal situations like this and see people so happy, it makes me compare my life to theirs and I see myself lacking so much it only breaks my heart. I have no one to spend holidays with. I usually volunteer to work Christmas and Thanksgiving because I never, ever have plans to spend these days with anyone. I will probably never get married, and my birthday is one of the loneliest days of the year. While I do have friends, I want so much more for myself. I want people to be close to me and to love me. It's a rough feeling. You're not alone.