Am I a nasty Cow? What should I do in future and am I at fault really?

That just sounds like a bad friendship. You might go to her out of habit also because you have known her so long you just feel comfortable with her all ready and go back regardless of the situation. If You guys honestly have nothing in common, she mistreats you and doesn't listen sound like their is no reason to stay friends. This could also say something about the other relationships you make with the opposite sex. Seems you might have or be creating a Self-destructive behavior. Both with staying with someone who might have treated you the same way(e.g. fiance) and your so called best friend. I Would say to you move on, she doesn't seem like a true friend, she just probably uses you for a self esteem boost. Find better friends focus on your self and improve how you feel about where you are in life and who you are.