Help! My girlfriend is insane!?

I'm 14 (almost 15) and my gf is 16. Last week at the carnival, there was this girl that was really hot. I didn't even notice that I was staring at her, but apparently my gf did. She just kicked me in the balls and started screaming at me in front of everyone! Ever since then she has been checking every text I make and being really defensive and b*tchy. I am thinking about breaking up with her, but I'm afraid that she might go psycho on me. Please! How do I either break up with her or fix our relationship?!?