Gf trouble

Ok im having trouble with my hopefully Girl friend see what happened was i was walking home with my ex boy friend and he said he was gunna get me back then when i was gunna leave we hugged and he KISSED me and i told My hopefully girl friend what happened and she sounded so mad at me i mean it least i told her!! its not like i kept it a secret for 3 to 5 days like some people do i mean she sounded like she was blaming me OMG what do i do!!!!