I have met her 3 week ago and we had four dates that week. The fifth we asked each other in the same time for a relationship.We both said yes after two weeks she told me that she laid to me and she is in love with another guy.She broke up with me and talked to her since then (one week ago).What should I do to get her back ?

So she used you as a break from her boyfriend or what? Why do you want her back -you never had her in the first place.

I agree with NoHelp4u. That you need to realize that you are better than that and you deserve someone who wants you and only you.