Jealous Boyfriend

My boyfriend and I have been dating for 6 mothns ALMOST 7 and I love him to pieces! But he gets mad when another guy says that I look beautiful, or when they message me on Facbook. I am completely loyal and don't message anyone back AND I tell him and let him see the messages. But he get soo mad and wants to fight the boy or go off on him. I told my boyfriend that he shouldn't be mad but be happy that other guys want me but he is the one that has me. I am very happy in my relationship but I just don't know what will get it through his head that people will say stuff like that all the time regardless is I'm single or not. We are both still in high school. PLEASE HELP!!!