What to do with this dumb bit**?

so there's this girl that my boyfriend works with, she has flirt with him and made some comments that have made me upset, for example one night he was hanging out with some coworkers and she was there, and he accidentally called me so i stayed on the line just in case he said hello or something but instead of that i hear the girl say so are you getting laid on ur birthday, and he said no cus its none of their business, so then the girl goes don't worry i got you covered..and its not the first time she had said something like that, i don't see the chick so i cant confront her about it. and she knows he has a girlfriend..she has also posted things on fb like,,ohh just hung out with my favorite person, he makes me laugh, wish when we are alone you would kiss me, and other things..is it wrong for me to tell him not to hang out with her? even though there are other people around,??