I totally understand. You must do what is best for you. You get to choose who you hang out with and who you let go.Good on you both trying to keep the relationship going but than realizing you must put boundaries up. I've lost best friends for way less damaging reasons and the behavior your friend is putting up is pretty toxic and only she can help herself, which sad to say she probably won't and to walk away to protect yourself is the best brave move you have made.
And yah past friendships mean no obligations, something I've been dealing with a lot lately as I was always the one trying to maintain relationships where the responsibility was always on me to connect. Im a nomad and move around a lot and seems like being the person away from my real hometown or adopted town means Im the one who seems like is expected keep the communication going based on when I come home and if I dont reach out to the zillion people I get wrecked with anger because I dont contact all friends when visit home (usually only ones that I keep up with).
Letting go of my old friend was tough. I had good memories of when we were young and hung out together. But, dropping our friendship is for the best. She's become a demanding taker. At first, I thought I could help her. Then, I was quickly tired of giving to her while she wasn't helping herself. I realized that I wasn't helping her -- with every handout, I was enabling her to be irresponsible. I wouldn't do that for my grown kids. Why would I take on an old friend?