It's never 100% a result of "illness", that's a cop-out. We always have choices, sometimes they're hard, but "using" someone takes time, isn't just one ill choice but a pattern. One can apologize and try to make up for errors of the past but one can never go back; if you disappoint someone (as your friend did you) you can't make that like it didn't happen. But it doesn't sound like she's even saying "sorry" and trying to make things better and it's too long and she's not as sick now, etc. Let her go and maybe, if as your other friends say, she later sees she made bad decisions and choices then she needs to come find you, not the other way around! YOU have done nothing wrong.