I think you're doing a pretty great job describing your feelings, both here and in other posts. I'm so sorry this is the way that you've been feeling, this and the other things you've been talking about. This is so much to carry. I get it, I'm someone who was also carrying a whole lot -- including a lot of trauma, a lot of depression -- when I was around the same age you are, and I can totally relate to having felt some of the ways you've described. Wanting to go back to a time before trauma hit and before other responsibilities and expectations got piled on is so understandable, especially when you're in a depressed and traumatized state AND not being supported. Heck, wanting to go back even in the best of circumstances is understandable.
Like I mentioned in your other post, some of what I hear you describing here is severe depression. Some more is grief, some more is trauma. And absolutely, it is hard as hell to live the way you're living right now: massive kudos for surviving so far. That's a serious achievement, truly.
I know that right now, while you're still so depressed, doing anything might be really hard to drum up the motivation for, but I wonder if you can't maybe at least start a list somewhere of some of the things you feel like you missed out on. It might actually be that either now or later, you can still do some of them, and even if some of those things are very small, making a practice of doing them for yourself when you can might help you out when you are feeling like this *and* give you a little motivation sometimes, which might be a way to just take care of yourself, period, you know?
How else can we help support you in this?
Never doubt that a small group of thoughtful, committed citizens can change the world. Indeed, it is the only thing that ever has. - Margaret Mead