I stated to hate my "best friend"

She drives me crazy. We've been friends since we were kids... our parents would go to the same pool, so we'd always play together. She was a grade higher than me in school though, so in highschool, we never really talked. We would pass notes to eachother, but she'd always talk to her classmates instead of me. When we werent in school we'd drive around places and be like normal teens. It was a lot of fun! But when I started dating, and she wasn't... she started to meet guys online. They'd take advantage of her... one didn't have a job, or a car, so she drove him all over the place and she ended up loosing a lot of money out of that. I tried to tell her to get away from him. She never took my advice. He ended up in jail, and she still visited his family. They'd tell her that they can't wait until they get married and have kids. i told her that they're just gonna take her money. She said she knows but she still wouldn't break it off with this guy. So I was telling a coworker of mine who was in his 60's about this situation and what I should do, because he was really easy to talk to and he listened. So me and my friend were at a farmers market and he showed up because he knew we went there often. I told him he should talk to her and try to explain to her that this guy was bad news, because he was really good at talking to people. He talked to her then, and they exchanged numbers. And I thought "great!" because I thought she would finally listen to someone. Then one day I asked her what she was up to if she wanted to hang out. She said no, because she was with this old man. And when I read that I thought nothing of it, untill she texted me back saying, "No, I'm WITH him. We're together". She is 24. He is 64. You can probably sense my problem with that. He was using me to get to her for some fun. She never thought about how I'd feel about it. I told her I didn't like it and she totally flipped on me. She sent messages to me and my mom, over the phone and on line, about how she's gonna make my life a living hell and all kinds of nasty stuff. I had to block her off everything. This went on for a few months. Then it was quiet. Then she started messaging me again like nothing ever happened, saying we should get together. SHE NEVER APOLOGIZED. Now, this friend has maybe two friends. Me and another girl that she said she doesn't want to talk to for whatever reason. So we hung out a few times. It's never been the same as it was when we were kids. Now when we make plans to hang out, she always backs out. Makes up an excuse not to. And every night she messages me on fb either through chat or mail, that she's going to bed. I'm getting really sick of her games. But I don't know how to tell her, because she goes psycho on me. What should I do? It's really been bugging me for a long time. I feel guilty then also because she has no other real friends. I've been her "best" friend for the longest time. People have told me I'm too compassionate towards her. But it really stresses me out because she never acts like a real friend. And, she's still with this old creep... which is causing problems in his house due to his 30 yr old son still living at home, and problems with her family because her parents want her to have a normal relationship. She has always had low self esteem... that's another reason I feel bad. But what should I do. I'm sick of feel bad. I'm sick of being tossed around and used. I wanna tell her to get lost, but I'm afraid she'll go nuts on me again.

The thing about her telling me when she's going to bed is... she doesn't say anything else that day. All she says is "I'm going to bed. Goognight." Isn't that kinda odd? I don't say goodnight back all the time, just when I'm in a decent mood.