How do i get rid of a girl that is trying to steal my man cause she is jealous of me an my bf?

ok, their is a girl that i hate, her name is allyson, well she is always mistreating my "bf" an it gets on my nervs, shes always telling him that she loves him and then the next minute she trys to make him feel bad, well i told him(my "bf") that he needs to tell her to leave him alone or i will but he doesnt want to hurt her. well i want to tell her that she needs to leave him alone but if i do than he will get really mad at me cuz me an her get into fights alot an then she starts ******** to him sayin im startin **** w/ her, which im not, an idk how to tell he to leave him alone w/ out makeing him mad at me, plzzzz help me!!!!!!!!!