I have not been to DBT in particular and so can't speak for it. However I do relate to your experiences.
I have been to therapy in general (not for BPD but something else) which was similar somewhat to CBT. When I first met my therapist, she told me that she will first take me through sessions to "open my mind" to therapy. Within a month of sessions, she said she had realized that I had, infact, come with an open mind. ( I must confess that for the first few sessions, I did play mind games with her until I realized that it was not useful to me.)
Within 5 months of sessions, I had begun to realize changes in how I saw life and at the end of 5 months, one day, I told my therapist that I didn't need her. It was a compliment to her and she was very happy for me. Then I was out on my own trying to put into practice all that I learnt, with occasional meet-ups with my therapist just to update her about my progress.
On the first day of therapy, my therapist explained to me that her role was merely to guide me on the path to unlocking my own potential, but that the potential and the ability to realize it lay within me. I kept that in mind during the whole 5 months.
In contrast, a person I know (who is an N) went to the same therapist roughly during the same time. He became extremely bitter with the therapist and left therapy in one month. He even went to the extent of smearing the credibility of the therapist to others. ( I am not sure who lost and who gained in that effort.)
My learning about therapy is that it shouldn't be treated as a "quick-fix" or "medication" as if it can cure you of all your flaws. Neither can it provide a easy-to-use checklist that you can just bound yourself to. Nor is there a guarantee that within a specific time everyone will have the same level of recovery. I went into therapy with the spirit of self-discovery. My therapist was merely my guide who opened up new possibilities for me. But the hard work, responsibility and commitment was mine. I owed it to myself for my own well-being.
I don't know how each of your specific situations have panned out, but you may be able to relate to this experience of mine with therapy.
I don't have family/friends that support me, either. My family doesn't understand and I don't have any friends.
brokenopen - I understand this. My family still doesn't get it. But the point is that I do and that is enough. I don't expect everyone to understand, since its difficult for them.
I should look at it differently and try to do better than I have, admittedly...it's change...it scares me.
That is a start you have. Its true that change is scary. But I have realized that it was my own fear that kept me from facing the world without fear. And the fear of change was perhaps the biggest fear.