What exactly did u mess up? Seems to me that your ex messed this up. You should probably cut communication completly with that knucklehead and quit letting her dictate your life..... She is not with you anymore man, I wouldnt even put up with that garbage if she still was.
It seems like you are just lusting after this other chick pretty hard, Id leave her alone just because she is connected with the ex...... Plenty of other females out there just as good as that one. Do what you do though.