You say that she's the one that broke the friendship 6 years ago. Why didn't you break it long before then, if she was all that terrible? If she hasn't changed, then you're in for more of the same. You dealt with it in the past and didn't seek to break from her, so what makes it any different now? Now if you had been the one to break it 6 years ago, I could understand, but you didn't.
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