i want to leave my bipolar/depressed girlfriend but im affaird she'll hurt herself

I've been with her going on 5 years we have a wonderfull 3 year old girl. the first year was great she was not on medication. But it seems shortly after I proposed to her, things went left instead of right. I approched her about it as nicely as I thought possible and she flipped. I never seen it coming I didn't know what else to do I called her mom. She calmed, she got help and still even with medication she was having episodes. It gets really bad. I've asked her to leave 3 times now and every time she tells me she has nothing to live for... so I tell her to come back. I need out.. the stress and fear of looking at or answering my phone or coming home to nothing but bitching is not only unhealthy for me but our daughter as well. Are little girl should not have to see or her these episodes but I also don't want her mother to hurt herself. She was 302 by her mother when she was 16 she was diagnosed with bipolar/depression. The poor girl losed her father at 4 years old when he took his own life. I can't deal with it no more, I want out but how?