The thing is, BPD isn't dependent on whether you have or don't have relationships. The traits of BPD affect how you handle relationships but no, it doesn't require it. Another thing is that like Mara said, the fact you dont' have relationships can be a part of the BPD Dx. I guess what I would ask is, why you don't have many friends. That could say a whole lot toward or against the dx. Me personally, I have next to no close friends IRL. Almost all of them are online and even then very few are close. My reasons for that are because of my problems with people and distrust, paranoia, fear.. and so many things that have happened to me in relationships, which, all point to BPD for me. That would be a better determinant for you and a better way to look at it.

BPD devoid of relationships still exists, but the symptoms may be a little subdued because so many of the traits affect relationships themselves. That may be why your T or Dr recognized the BPD but you don't see it.

Hope this helps! *hugs*