Problems about my girlfriend? PLEASE NEED HELP?

i got done with athletics and then went to go see my girlfriend i walk up behind her and shes with her ex boyfriend and i see them hug each other around the waist she said it was just a goodbye hug and the thing is she has given me one hug at school when he told her to because she doesnt want to get in trouble but that just pissed me off seeing them hug i love this girl and she said she loved me what do i do in this situation i told to dude dont hug her again and he said he wont