carm,
Gosh, I'm sorry you're hurting so bad...
I know many of us are here for you and we understand, this you already know. You are not alone, this you already know. Your needs for support will be met, but again, you already know this...
Ranting, or venting is healthy. It does feel as if progress often slips back into that dark place. No way out, except those horrible thoughts keep leading us to...escape? the horrible alternative?...you know this, too. You are in it.
Our pain is added to more pain and suffering...our suffering leads to more suffering.
What I enjoy so far about DBT is it's eastern philosophical roots:
(Taken from a Buddhist site)
"Mindfulness may be described as the process of bearing something in mind, an awareness which does not drift along the surface of things but is a thorough observation, observing without judgment, without habitual reaction or compulsion, but clearly acknowledges what is actually there in the flow of experience, noting its nature...By strengthening mindfulness through meditation and maintaining mindfulness in daily life there develops a deep insight into the impermanence of phenomena...
The result is a state of being where there is no need to react to the craving, as one knows it, like everything else, will in its own time cease to be."

Remember, friend, this too shall pass...
If you once sought comfort in spirituality, perhaps you can delve deeper into this. I identify with many Christian, Buddhist, and new age beliefs. These beliefs often give me great comfort...if I'm present to them (which I'm generally not).

Sitting quietly in our own emotions and thoughts is SO devastatingly uncomfortable...a person without BPD could never understand. You may not be asking for unwarranted advice, so I can simply acknowledge your feelings, relate (I have been there many times before and still struggle) and reassure you that these feelings aren't permanent.

Remind yourself how hard you are working (you are inspiring me to work harder for one thing! I'm actually reading DBT stuff and I'm the procrastinator extraordinaire ) and you help many people around here. However, reassurance may not help you either, but I can offer it nonetheless.

Buddhist philosophy suggest we can end our own suffering via unconditional love. Christian philosophy says that we can end our suffering via God (who represents unconditional love). Certain energy and chakra based new age philosophy asserts that we end suffering via tapping into our 'postive and compassionate' energy and sending it outward via unconditional love. My program of recovery from alcoholism states that I can heal via service to others without asking anything in return (a form of unconditional love and compassion).

Before I can find unconditional love (toward myself, the world, others), I first have to accept that I don't have it, I am in pain. I have to accept that I can't change things that happened. Things I did or things that happened to me are out of my control. If I feel pain, this will cause more pain and it will perseverate on and on and on...suffering will continue and cause even more. I have to accept that I am in pain before I can change it (even if I can't do it without judgement yet) the same way I had to accept that I am an alcoholic before I could do anything about it. (This sucks, I want to change it, I don't know how, but it sucks. It's there...)

You are accepting this, you're already doing it. Okay so we know we have a problem, we know there's a possible solution. We know it takes work, but that really doesn't help us. We're on the right track, but boom, our thoughts go back to that horrible thing, our emotions take over, our whole world is clouded in these thoughts...they hang over us when we wake up...Now we feel even worse. There must be a way to escape these feelings. But there isn't, but there is...
These feelings and thoughts are here right now, they're so uncomfortable and painful. And that's the answer. Simply sitting, breathing, quietly, feeling the pain, knowing the pain, accepting the pain...Label it "oh thats here right now, that pain." We don't have to do anything about it right now. Just know it's there, nothing can change the things that have happened. The future and past are irrelevent. I am uncomfortable. I am sad. I am hurt. I am in pain. I want it to end...it will, but I can't deny it. (The same way I can't deny my alcoholism). Denial is cause to drag past pain and future worry with us...acceptance is cause to be it and experience it. We're human afterall...pain is inevitable. It will abate on its own. I don't have to make a rash decision about how I am going to deal with this pain in a week or an hour. I dont have to deal with it at all. Just experience it.
You're already doing it! (By talking with us and seeing it and feeling it.) You've just given us a great gift.
(Sorry this is ridiculously long...)