Wow, I'm really shocked and sorry that you found out like this! I don't understand any professional who doesn't discuss their diagnoses with clients as a matter of course.

If you go to the borderline personality disorder section of the forum, there are some threads about books on BPD, with people saying which ones they found more sympathetic and easier to read. Sorry, I don't know how to post the links without losing this message! My personal opinion is that I would be very cautious indeed about reading random stuff online- a lot of the things said about BPD are deeply offensive (and often untrue) and at best very hard to hear, and I think it's best to read a book by a knowledgeable and sympathetic professional or a client who has experienced similar difficulties. Whatever you read, make sure it's recent- until the development of DBT and other successful specific treatments (schema therapy, mentalization-based therapy, transference-focused therapy), personality disorders were thought to be life long and untreatable, so a lot of the older material is very bleak indeed.

My personal experience is that I don't have a diagnosis of BPD, but I have therapy which is for BPD (DBT and now schema therapy). I would want to make sure that the therapy I was having had evidence of successfully treating BPD, but that's just me. However, before even deciding that I had BPD, I would want to have an indepth discussion with the psychiatrist who diagonsed me (and their reasons for this) and with my T who knew me well, and also make my own decision about whether it made sense.

I really hope this diagnosis, if you feel it fits, is helpful to you, and to your work with T