Cutting off a “best friend”

Have you ever had one of those friends you have known so long and been through so much with, that no matter what you’ve remained friends? Has that person ever become so toxic to you that you no longer feel you can keep them in your life? I have been hurt over and over by the same person I called my best friend. The last straw was when she told me she would help plan my baby shower with our other best friend. She blew that off. Then she said she’s sorry for being a shitty friend, tells me she will be at the shower, and blows me off again to go to a bachelorette party 8 hours away. No call, no text. I wasn’t even surprised but I’m still so hurt. I was hoping she would be there for me during the biggest change in my life yet she would rather go out with friends and get drunk. I don’t know why cutting her off has been so hard for me, but this time I really can’t keep allowing myself to be her friend.