Is it normal for your best female friend to act this way?

Me (male) and my co-worker / best friend (female) have been through a lot over the last two years. When our friendship first started, everything was fine. We would talk about past and current relationships, sex and give advice to one another about the opposite sex. About three months later I brought my g/f around her...she tried everything in her power to beak us up. It worked! The second g/f I brought around she gave her dirty looks, and blew me off! After breaking things off with the second g/f I remained single, still am! Now whenever I talk about another female she gets upset.

Within that year I found myself falling in love with my best friend. So I tried asking her out and she blew me off. Which she still does to this day. I bust my ass for her at work, buy her anything she wants, and treat her with respect, always there for her when she needs me. But she still won't give me the time of day outside of work. Our friendship just keeps going down hill. We fight like crazy now. As soon as we make each other mad she will distinctly blow me off and flirts with every guy right in front of me to try to make me jealous. She's even admitted this to me. What she doesn't see is how bad it hurts inside when she does this. For her birthday I spent three hundred dollars on gifts, she gave me kiss on the lips. Two weeks later we had an argument and told me she had no intention of leading me on and she doesn't like me. It seems as if nothing I do is ever good enough. I've already talked to her about the head games and that I like her. Haven't told her that I love her yet though. And if we don't talk for a long period of time she comes back and tells me how much she misses me. Nothing changes!! I'm going in circles. is it normal for her to keep playing head games and try to make me jealous if we are not speaking to one another?