How do I break up with my friend?

So I have known my friend Megan for almost 2 years. We met in an elevator that got stuck at a lawyer's office. She was there to finalize her divorce, and I was there to talk to my lawyer about some legal issues i was having, anyway... that following week end we went out together, and we really hit it off, and we ended up fooling around. She told me she didn't have any friends, and that most guys just want to sleep with her. I myself have attachment issues, so i told her I will be a friend to you. And I ment it. I gave her my word that I would be a true friend and i wouldn't abandon her. Now over the past 2 years she has tried to find a man online, but it was just one disaster after another. She gives her heart and body to easily to these men she meets online, who usually ditch her after they humped her afew dozen times. I keep telling her if you are too easy men will never respect you. But she doesn't listen. The type of men she goes after are so Douchy, and they usually hate me. I have even gotten into fights with afew of them over nothing.

However, its always the same cycle, she goes out and gives it up, and the next week she calls me crying, and I am always there for her emotion support. But i can't do it anymore. She doesn't follow my advice, and I love her. Not in the sexual sense, but in a different way. Its hard to explain, but it's just too painful to see someone you care about continue to hurt themselves.

I can't do it anymore, but I am conflicted becasue i think I am the only friend she has that she trusts. She isn't from the city we live in, and when she is not out at the club when some john from the internet, she is at work or at home on the internet. She has 5 dating website accounts. I have tried to introduce her to my friends, and to good men i know, but it never worked out. All she does is complain about men, and she tells me its their fault, but i tried to get it through her head that is her fault. The men she goes out with are the wrong type of men, but she won't listen. So i want out of this. Like i said it just hurts when someone you care about keeps sabotaging themselves. Advice please?