I think that there's a really powerful and painful irony at work here that makes the whole thing even more sad. I want to break this down into pieces, because the whole thing seems to hurt so much that I find it hard to think about, and I'm at a pretty safe distance, really.
AFAICT, the sequence of events is:
- She had a best friend for 8 years and didn't include you in that relationship in any way
- She introduced the two of you to each other, you found out that you'd been excluded, and that discovery was very painful
- You responded to the pain by expressing the pain to your family in ways that probably caused them some pain
- A cycle of revenge seems to be getting started.
The irony is that at step 2, she was starting to include you in her life more. At step 3, I suspect that the family is thinking "Well, that went badly."
I think that this is how PTSD traps us and can isolate us. We experience something more painful than we can possibly bear, which becomes lodged in our brains and makes us hurt more, which makes it harder to handle any further pain, which means that the pain is more likely to get stuck, which makes us hurt more, which makes it harder to handle any further pain....
I know that when I'm in more pain than I can handle, I can do some very conterproductive and destructive things (although I'm doing better). You've admitted to screaming at your family - if they screamed at you, would you avoid them? I suspect you would either avoid them or fight them.
I think the whole sequence of events is a tragedy. My hope at this point is that things will settle down, which probably means everybody leaving each other alone for a while. I know that my efforts to fix things when I'm in more pain than I can handle have tended to make things worse. I suspect you're currently in more pain than you can handle, and I suggest you don't try to fix any relationships until you have some spare strength.