Should I walk away or try to help? And how do I do either?

I have been dating this girl for 6 years. Our relationship was never really stable. I cheated six months in and she admitted she lied about her past. We went back and forth doing things inappropriate in the realtionship. We bought a house without being married because of the tax credit. We had planned to get married when we both go our stuff together. We would spend every moment we weren't at work together. This summer I had a business trip for 5 days when I returned I learned she was contacting old boyfriends and drug dealers. It got worse when she started going to the bars every weekend. When I told her I was comfortable with that she did it more and didn't care. She ended up meeting a guy and lying to me about him. At that point I ended the relationship and we have been talking ever since. Trying to figure it out...three days ago she calls and tells me she slipped up and got high on meth. She has since told me she doesn't like it anymore and wants to be together...I don't believe her but at the same time I want to help her get clean and healthy. She lies about everything and plays with my emotions. Do I cut it and run or do I help her thru these breakdown?