What else can i do???

ok well my gf talks to this one guy i really really hate! i have my reasons! ok well he txts her like for example... Hey y!&...Leave ur bf n come with me... & Do u really like him!.......... n other stupid shitz like that! i really get pissed off with this guy! i have never liked him even before me n my gf started goin out!... so my girl doesnt want me to do anythin to this guy! She says hes her friend! well i get jealous like always, i mean who wouldnt at this! i believe this aint right for him to be txtin this stuff to her! I just dnt want her to talk to this guy n she wont stop!... like if she tells me not to talk to sum girl she dnt like i stop! but if i tell her she wont! n that really pisses me off! Then we end up fightin! Well i dnt wanna break up with her cus i really like her alot! Wat can i do to make her understand that i dnt want her to talk to this guy???