Most Helpful Girl
All I can say is: move on. You could talk to her to see what you did wrong , or what you did NOT do. Communication is key in all human relatioships. If after you talk and can't figure out what went wrong, well... there are 3 hypothesis:
1) she probably overthinks things and goes nuts over them for no reason,
2) she did something bad and reflects it on you,
3) she just wanted to find a sketchy excuse to dump you and leave you dumbfounded.
But still, I'll try to find out what went wrong.
Most Helpful Guy
Usually, they want an "emotional" connection with a guy (fairy land style), and then get upset their emotional "needs" aren't being met. She believes you don't get her, so she starts feeling more distant--and more bitchy. Her increased bitching makes you distant in turn and you stop trying, which she then interprets as you no longer caring about her (which is now, in some measure, true), so she goes into one last tantrum to "fix" things, then flames out of the relationship.
Ultimately, she brought unrealistic expectations into the relationship, got herself disappointed, then blamed the guy for not being like the guy in her imagination. Thus most breakups.
That said, it couldn't hurt for you to analyze where you may have legitimately fallen short and make sure it doesn't happen with a future girl (hint: learn how to help a girl be realistic without having to logically explain it to her).