What can i do? (doesn't just have to be how to confront her)?

So theirs this girl her name is Ariel and I told her i like her and she said their was another guy and i said for her to save me a place after him this morning i found out that shes been going out with a completely different guy for 3 days. Now I'm mad cuz she did'nt tell me i found out over Myspace.Now how do I confront her without being a ?(keep in mind I realy like this girl)