First, I'm going to tell you to take my words with a grain of salt or pretty much don't listen to me at all because I myself am a bit of a relationship newb.
Now my advice:
If it didn't work the first time, it won't work a second, third, fourth, or fifth time, as you have yourself seen. That should be a red flag to you, that this person is not committed and flip flops on what her feelings mean. Now of course, in some instances going out with a girl a second time might be okay, perhaps your first relationship ended on circumstances not necessarily ordinary. But if it breaks down again and again, and you keep trying to rebuild it you will only exhaust yourself, and you break each other down in the process. You need to find someone who cares enough for you that they will fight with you to sort out the source of the problem, so you don't have to fight any more, and continue the relationship. If the you can't sort it out... then well, it was not meant to be, so don't try to make it out like it was.
If I offended you at all, please let me know, it was not meant. The conversation though is touchy as it is, so again remember that I'm trying to help you.