<human>: Can you give me a shortened version of the text?

So its been a year and a half, not too long, but long enough that i believe we were getting some traction. It began at 8 months into our relationship, when some random person(lets call him bob) told her that he liked her and wanted to be with her. So, she came very sad to me and teary eyed, telling me this. (i had previously warned her about bob and she chose to not listen to me anyway). I told her not to talk to him, because i didnt feel comfortable with it, and our relationship continued, better than ever.
      Or so i thought.
So i mean months pass and she starts to slowly distance herself, ignore me, she even flinched from my touch. And so obviously, i needed to confront her and so i did. And she said she doesnt know if she feels the same. And so many tears were drawn, a lot from her.  Then, my friends tell me, apparantly bob had never left the picture. So we break up.

But only for two days, as she comes to me, absolutely sobbing, cutting herself mind you, saying she misses me, and she regrets every decision she's made. Please mind that this is my first real relationship, and i wanted it to work. I give her a last chance, we stay happy for two months. And now we're here. She's talking to bob again. But now she is always depressed and always asks "why would you stay with me? All ive done is hurt you and you still want to make me happy."

(back story- the entire time we dated from the 8th month to the 13th month, she went behind my back, kissed bob, hung out with bob, when we broke up, she went to bob and then came back to me)

What should i do?
Obviously, this will not end well, so what ways are there to heal and lessen the pain afterwards?
Please note, i never want to hurt this woman, she's held a very special place in my heart. And as of right now she still does.
<bot>: girlfriend continues to cheat on me, i dont know what to do, given her many chances, she's lied many times, what do i do.