I get it. I'm with you. Been there, done and doing that. I can see a lot of my actions and responses in what you are doing, and could have written nearly the same posts.
It is SO completely frustrating. I've done that I don't know how many times. When you invest your time in these things, and put yourself 2nd, when the end result isn't what it should have been, you're back at square one.
I, now, am at the point where I just don't budge. If she's going to do something - great. If she wants it bad enough, she'll get it herself. She's getting her booze, drugs and fake nails somehow. She can get her pants, ID, whatever. At this point she's gotten so many IDs, pants, shoes, work outfits, and has NOTHING to show for any of it. NOTHING. No lasting jobs, NOTHING. Just food stamps. She can get those just fine. I feel badly. Unsupportive. But, today, right now... I'm in self-protection mode. I truly believe if she wants it, when she decides she does - she won't be stopped. But, as long as (my kid) is calling me and wanting me to set aside my life for her needs, and that is the pinnacle of her success, I know it won't work. That's the cycle of codependency that we're trying to break. Been there, done that, same result each time. She says I'm abandoning her (and that's what my gut feels like, too), but in our situation, I'm trying to allow her to grow. Extreme situation, somewhat extreme reaction. I don't think anyone who hasn't raised a child who is a GFGx3 would understand.
Not saying this is the formula for your response, but it's where I'm at right now.
Hang in. I feel for you.