Try to open up your mind bro. If she keeps on doing this to you, it only means one thing, she is not into you anymore and she has someone else already. BP is right, she is treating you like a dog. Don't allow this to happen. Fuck up things are enough. Don't let her add more.
When woman flakes to me she does it three times (first, the last, and never again). Ignore her totally and break up with her, you've had enough of this.
I knew a man who broke up with his gf with a simple sms "we are breaking up, I'm seeing another girl". ..it hurt her, though she planed to do the same thing to him. It came to her unexpectedly and she thought he wouldn't dare to do that.
Take Bill's advices.