I had a best friend for about 10 years. we're both early 20s, so it's a decently long time for us.
What happened was we developed feelings for each other and started dating.. she cheated and ran off with a guy and turned mean as fuck. later on around this time last year something happened and we reconnected, and stupidly I forgave the whole ordeal on the basis that she was my best friend for so long, and she promised never to do anything like that again. fast forward to the beginning of this month, and guess what happens? Same guy, he spent a year circling like a vulture waiting for me to slip up once. Out of the blue too, we had plans to move in together early 2015, there was talk of marriage. It sucked. She blamed me for little issues that would have been easily remedied had there been any attempt to communicate them to me.
once again she became mean, rude, intentionally cruel. she felt nothing whatsoever for me, go on about how I was always such a horrible friend and boyfriend, and my mere presence seemed to piss her off and annoy her, she'd yell at me for anything or nothing and spent all her time with this guy while fervently denying there was anything going on. which of course, along with the fact that she was talking shit about me behind my back, was all found out via multiple mutual friends.
And when she got my xmas gift, (I put together a big care package for her while we were still dating, we live decently far apart so seeing each other as much as we would have liked was a bit of an issue), she went on about how terrible of a friend and boyfriend I was, and I got a nice "LOL THANKS FOR $600 WORTH OF SHIT FUCK YOU HAHAHAHAHA"
She was my best friend and also the one person that could utterly destroy me, and she did, so I made the choice to cut her out of my life. I miss her like hell, but I also know I'm better off.