My friends boyfreind is messing around and she wont believe me?

AT lunch at school yesterday my freind wasnt there and a girl kept messing with Her Boyfriend Carmelo and i tryed to tell her what happened and more that had happened later that day. She said that she will talk to him but at lunch he said that i was a lyer and she believed him and my other friend told her that it was true but she still didnt believe any one i dont want myu friend to get hurt by her dumb *** boyfriend.