She is testing you, to see if you love her "enough". You giving up says to her that she is unloveable and unloved.
What can you do to change how you feel? Tell her how you feel. How much it hurts you and how much you care and how unappreciated you feel. I agree with Lisanne; decide which way you want to go, and then don't back down. This is just eating you up, I can tell. Been there, done that. Set the boundries and make them rigid, or set her free. My heart goes out to you.
YTQ