I'm so sorry you're going through such a hard time. And I'm sorry the support group isn't working out as you might wish.
I'm with you on the horribleness of our society and the fact that family can be such a total downer and waste of energy.
Just know that you're not insane. You're going through a dark night of the soul. Try to sit with it and quietly watch the feeling that flood you, looking at them like waves of an ocean that you can learn to surf. That energy has tremendous power. Try to use it to reach out and make something.
You're wrong about your writing being wrong. It will be always be right. It will always say exactly what you were going through at any given moment. It will always reflect that truth of your experience back at you.
And you can use it to start to shift things. To let the load lighten a bit and move further from pain to that other side of the dark night of the soul, when the dawn comes.
I've been through this, too. I remember what it was like to be twenty and to be so full of despair that I'd go to dangerous bars and look for fights just to feel something real. I remember the terrible ache of the overwhelmingness of facing the fact that I felt so totally fucked up that I couldn't imagine every being right in any way. I remember feeling so full of anxiety that my stomach was constantly bad and my energy was constantly like the electrical sparks in a mad scientists lab.
I also know that feeling will pass with time and with the work you're doing writing the stuff out and going to the group and just being with the pain for a while. I've been there, too. There really is a dawn. Please trust that that's true and that the dark night you're going through can actually leave you very, very strong.
Know that the abuse is over. And know that even if you don't see it fully yet that you're fundamentally OK. You're not insane. You're just in a deeply powerful place where your emotions are strong like they'll never be again. That energy is a powerful source to channel. If you every wanted to make some art take the pain and make it work for you.
I'd also suggest sharing your note to us with your group (just go ahead and print it out and read it to them). I'd be willing to bet that those other survivors could really use some heartfelt words. And I'd willing to bet their responses would be warm and kind. One of the benefits of working with those older guys is that they'll have some distance from the abuse that you don't yet have, and that distance can help you heal.