Friends lie too much?

well my best friend for 4 years messed me up this year she started to hang out with this new girl so we became friends with her i didn't like the girl at first but we cool now and then my best friend start hanging out with this new grope of girls that I didnt liek and we ahve been fighting cus of that for a long time now she dosnt tell em thinsg and lies she dosnt tell me what happens even thought she does tell teh other girl who ahtes her and donsnt even liek her what shoudl i do?