Why did she do this?

There is this girl that liked me for 8 months and we talked and flirted.. we talked to each other on the phone everyday all day. We hung out as well. She than admitted to have feelings for me and that she thinks she would be happier with me than with him. He had proposed to her and i told her i was gonna go because it was not fair to me, she GAVE BACK THE RING FOR ME! Her friends found out she liked me and she denied that she did . She than became really distant with me and cold to me. When i decided to back off she cried and begged for me not to leave but than go right back to her being cold. Than she tells me she needs time to think. A week later she calls me saying shes not happy with him and wants to be with me. Nothing is done. She goes back to being cold . Than we get into an argument because i tell her im tired of being strung along. She gets upset and says im hurting her and that she just wanted to be friends with me and that she never flirted . Than the next day she says im important to her and she has FEELINGS for me. Than lastly she stops contact with me all together and its been 1 week now.. what happened .. we are both 22. And my friends are saying she will be back. I highly doubt it.