Ending my friendship?

Can anyone actually say that there friendship had so many problems to it because of a guy,that dated your friend and then fell for you? Well thats a problem I have been in for almost four months,and I must say it's gotten me a complete emotional wreck. Lately I just wanna tell her I am done being her friend,all she does is complain that I want to get back together with my ex-boyfriend,it's not her decision, if I am happy with him,which I am so so much , I will give us another try,though we have broken up 2 times already,you know that saying 3rd times the charm,lol. Which I definetly believe in because I have this feeling when we do,katie will be out of the picture, ever since I broken up with him our friendship has turned into a complete mess,we argue more,we barely call one another. It's all there our friendship is ruined,but I know this sounds cruel but, I am glad my ex-boyfriend came in between our friendship, he's stuck up for me,and I can't stand up to her. She has never been a true friend since a very long time.