Should i try to get my ex back?

Me and her met texting. She said she liked my best friend and i asked her if she really did and she said yea. We talked all night until around like 2:00 in the mornin. the next day we all went skating and i saw her the first time for real and if there was such thing as love at first sight tht was it.She was beautiful,sweet,funny,and shy. we had to leave and the next day i gathered my courage and asked her out and she said yes. we went out for awhile and i lived in Louisiana and she lived in Alabama but my family lived in Alabama and i visited a lot so i had chances to see her. the last night i saw her we were all at skates 280 and a little while before she left we were holding hands skatin around the rink and talking. when she had to leave we kissed but sadly it was just a peck . we talked every day a lot and i truly loved her. and can honestly say i know what love is like. while my sister and her husband went to a weddig i talked to oe of my friends and he said my best friend and my girlfriend were going out and she was cheating on me. my first reaction was anger i asked them over and over but they said it wasnt true. i broke up with her and she still wouldnt admit it but eventually she did. my second reaction was sadness i felt like crap and didnt know what to do. i still like her a lot and she says she still like me a lot even though she is still going out with my best friend. she said she would dump him for me if we could see each other more and says she feels horrible for doing that to me and would take it back if she could.what should i do ? i am 13 and she is 11. i just want someone elses opinion on this kind of subject because im not the best at these kind of things. should i try to get her back or totally move on all together?Please help