I Have To Say About Dating And Relationships

At break time in school today i was hanging around in the corridor with my girlfriend's best friend alone. We're pretty good friends too. We were talking about some stuff and then we sort of just sat there for a minute. It was kinda awkward and I don't know know why because it's not usually. She kissed me but I pulled away like straightaway. My girlfriend literally walked in at that moment and I tried to explain that it wasn't what it looked like but she ran off and didnt talk to me for the rest of the day.