Amelia, I have no wisdom to add to what all the other warrior parents have already told you. However, I can relate to the level of energy you have exhausted in your search for answers, your frustration, disappointment, anger and sorrow.
they really can't understand how stressful it is and the struggle to stay whole and healthy while your grown child's issues are constantly eating at you.
The above statement is certainly one I can understand and have empathy for. I think we all can. I am on a vacation after many weeks of dealing with my adult daughter's latest dramas. She is mentally unstable, makes horrible choices and is presently living in her car with 4 cats. I have long periods of time where I can put it all aside and enjoy myself, and then like an avalanche it comes barreling in out of nowhere......... My only child is living in her car and I am on a vacation. Detachment is an interesting path for all of us, the ability to systematically disconnect from the person you likely love the most, and stay away as they make choices which put them in harms way, or at the very least, keep them stuck. For me, it goes against my perception of motherhood. And, yet..........what can we do? They are adults, they are making their own choices, good or bad, right or wrong, it is now up to them.
I understand your fears about what will she do when you are gone. I have those too. When is it going to be the last rock to turn over to try to help them. Or is there no last rock, is it forever? I don't have any answers, but I can send you hugs and lots of empathy as we all can. That makes a huge difference too. I wish peace for you, moments of calm in the stormy sea you are thrashing about in, strength and courage to stay the course and my heartfelt prayers for you and your daughter to find a way through it all. You are not alone. We are all right here with you.........