How do i get rid if this female who flirts with my guy, and asks him out, even though she knows we are dating?

and your so called mate jack as well by the looks of it as he obviously isn't a good friend for saying all that stuff , if your boyfriend refuses to stop talking to her then you cant force him but i would rethink your relationship maybe with him or as hard as it may seem don't say anything and maybe let him find out for himself what a loser she is