"She was always there for me, talking me out of more suicide attemts, etc. And I'm going to be there for her. She needs help, and support is sometimes what people need most, something I didn't get during my problems."

You can be there for her and NOT be in a relationship with her. It's called the friend zone and she definitely needs to be put there until/if she sorts herself out. It's up to her and you sticking around and playing into her tantrums is only going to make it worse. She sounds like a very weak person that needs to learn how to be strong by being more independant. You can still be there for her as a friend but I don't think being in a bf gf relationship with this person at this time is advisable at all.