It went from "you're the man of my life" to "I can't live without you" to "I need you" to, well, she clearly don't care about me anymore. All these in about 6 months, for no particular reason that I can think of. 

I gave this girl so much time, effort, love, money (indirectly)...I have and would have done almost anything for her. I never got any gratitude back...and I still refuse to say that she is a bad person. That really is the worst part actually, I know that she is a good person but why did she use me like that? Why doesn't she care about me anymore? I'd do so much for her and she wouldn't even bother to say thanks. She would never offer to be there for me, but she'd constantly ask me to be there for her. That's so f*cked up.

Why do I love a girl like that? It's not even about sex since that part was pretty much gone after the first 2 months or so. On paper she was pretty much the worst thing that can happen to a man, but I love her. Why?