I used to think the world of my girlfriend but today...

Okay so im 15 years old and i used to think the world of my girlfriend but today i talked to her for about 30 minutes... She seemed mad at me for being no reason... I was trying to be nice... But i got mad... And then we just went about our day... But before today theres a guy thats in her class for the rest of the year and he text her a while back and told her that they needed to hang out and she told him that she had a boyfriend and he apparently didnt care... He then told her that she needed to dump her "little boy" and go out with a real man and then tried telling her that he was just kidding and im not a little boy i could lay him out... Im a freshman and i garrentee i could kick his ass... Im the strongest kid in my grade... I treat my girlfriend like an angel! Im romantic! I try with everything i do and i dont know why i deserve this... But she was talking to me today when she came over... We didnt talk until about an hour into the movie... She then asked what was wrong and i tried to hide it from her cause i didnt want her to worry about it but i couldnt make a smile so she new somthing was up... So i told her i didnt trust him and she said well you trust me right and i told her i did but not him... And she asked if i thought she was stupid and i replied no... She later in the convo said that she wanted to talk to him and asked if i would care... I told her i wasnt going to keep her from it but im really scared... Like im panicing... I dont know if i even trust her anymore... :'( and in the conversation she said that she was sorry and i was mad at the time and i told her not to be and she was like well i am and i told her not to he but i dont know what i did.... :'( im sooo scared of whats running through my mind... I havent even been eating much lately... I try but i just cant...