How do you walk away from a relationship that you know might never get better, but you're still in love?

I've been with someone for 5 years now and in the beginning things were wonderful. I thought, "this is the one." Things between us progressed so quickly; so much so we talked of marriage and gave promise rings the first month we met. It's sort of ridiculous now to think back, especially because of how our situation is currently. To make a very long, tumultuous story short, my partner felt threatened by a best friend I had. For 2 years we fought back and forth about "removing" that friend from my life. After 2 years of constant fighting, I gave in to her demands and ultimatums. Then it became about us living together. We fought about that, I again gave in, left my city, my home and moved in with her. After years of trying to change for her, it still seems I'm not giving enough... For over 2 years, we haven't had sex, as she states, she can't because it's emotionally too painful for her. Mind you, the reasoning has evolved over the years, but that is what she is claiming at the moment. I don't know what to do. I love her, I want intimacy and I want to feel loved back. There is no worse feeling than to be in a relationship yet feel so lonely. I feel resentful for all I have done, given and given up in order to make things work with her and all I ever feel is penalized. I've had things taken away from me like punishment.. She continues to live her life in "our past" which is the reason we still fight over situations that happened years ago. I feel so angry and frustrated, but when do I get to "get angry" about our past, too? It's unlike me to quit on someone or a relationship, but I know the answer might be obvious to some... Does anyone have a glimmer of hope for me or maybe some good advice?