To the person with BPD,First of all, know you are not alone. There are men and women from all walks of life who can identify with those three letters, and though they may not always be people you would choose to have in your life, they are your allies and your kin. We walk these paths together; and as lonely as it can be, because of that we are never truly alone.
Know that when you research your condition, you will come across websites that call you evil; you will come across websites that claim you are narcissistic and lacking in empathy. Know that being diagnosed with BPD does not equate to these things. Being diagnosed BPD means many things, but know that it does not make you a bad person. No website calling all people with BPD 'evil', 'manipulative' or 'narcisstic', or calling for extreme avoidance of all those diagnosed, is professional or accurate.
Know that your future is not assured. BPD is, technically, incurable -- but it is not a life sentence. There is treatment available and life can get better. If you have done DBT and found it unhelpful, know that there is more than one option out there. There is no such thing as a one-size-fits-all treatment for BPD, no matter what anyone tells you.
Know that your feelings, as strong as they are, will dissipate if you allow them to. Your anger will fade; your sorrow will ease. Nothing lasts forever, and your feelings are not the exception to the rule. You are the emotional equivalent of a third degree burn victim but you have the ability to graft yourself with thicker skin. You can get through this.
Know that you can learn to control your behaviour. What you do in impulse now, you can learn to contain. Your angry outbursts, your uncontrolled spending, even your self harm can all become more controlled and can even be overcome entirely. It will take time and it will take a great deal of hard work, but it can be done.
Know that the world is not as black and white as you'd like it to be, but you can learn to be okay with that. Know that your instinct to cast people or events into categories on the extremes can be worked with. You will learn, in time, that nobody is all good or all bad, and that is okay.
Know that you will learn to know yourself, gradually. Maybe you will start with your favourite colour, or you will choose an animal to love. Maybe you will discover that you like your eggs scrambled, or you dislike jelly.
Know that sometimes people will leave, but it doesn't mean that you are being abandoned. Life is full of change; people move on, or are taken from us suddenly. Not everyone was meant to be a permanent fixture in our lives; some people will stay for a heartbeat, others will fill our hearts for years. Know that you can learn to be okay with the changing landscapes of friendships and loved ones, despite the pain.
Know, most of all, that there is hope. BPD is not a negative reflection on your personality and life can get better.