How do i get out of the friend zone?

I'm in love with a girl. The only problem is that she sees me as a friend and shes is still in love with her ex. A little while ago i was dating this girl who made her extreamely jealous. At that time she told me that she loved me. I told her i loved her too. She said that if I forgot about my girlfriend then she would forget about her ex who she has been dating off and on. So I agreed to this and when I finally broke up with my girlfriend she began dating her ex again. Now she only sees me as a friend but I'm not entirely sure of her true feelings. This has caused me quite a bit of heartache and I want nothing more than for her to feel the same about me as I do about her. I don't know what to do about this and any help at all will be greatly appreciated.