I'd say just level with her and say if she's not willing to get help or even try to help herself, then you can't stay together. If she was getting help or trying to help herself then you could be there every step of the way but if not, it's not your responsibility to fix her or carry her. You're not a therapist, and she'll end up anchoring you down and leeching off you, whether that's her intent or not. I've been in a relationship like that before, I spent 2 1/2 years being as patient as I could even though at times she even said she'd kill herself if I was to leave. It only gets worse, because you can only take so much before all that negativity starts to wear you down. Give her the choice, give her that chance to make an effort to get better, but if she's not gonna put the work in why should you?