What if hes dating Your friend that knows you like him

If your friend is being a slut and is dating him even though she knows you like him tell her about it.Say you know i like him so why are you even doing this.If she is a new girl at your school and you have only known her for a few weeks than be like you know ive liked him for a while so please let me have a chance before you take over and if she doesnt back off than try to show him that hes way out of her leage and more likely in yours.