When to break up with a friend?

Torrie
I've been best friends with this girl for the past 8 yrs. She's been in this awful relationship for a year, and I've always been there for her. This guy is possessive, controlling, mentally abusive, and very obviously cheating on her.
She's starting to change now, and it's starting to negatively effect me and her other friends.
She won't leave her house, and when she does, she expects other people to pay her way. (She doesn't have a job.)
I have some serious health problems, so I was sick for a while. She knew this, but decided to tell her bf I was blowing her off. He messaged me on fb and started so much shit between us. We managed to resolve things. She started downing my relationship. I am very happy and in love with a great guy, so there was no reason for this. She told me her bf wants to have her other "best friend" jumped for really no reason. I found out she was saying some rather not so nice things about me to other people.
I tried talking to her, but it does no good.
I know she's going threw such a hard time dealing with her crazy bf, but I don't know how much longer I can deal with this crap. I feel bad just abandoning our friendship after 8 years while she's so depressed. Should I feel bad, or just give up?
When to break up with a friend?
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