Leave or stay?

My fiance and I have been together for 5 yrs, I moved his daughter who is now 13 and him in with me 3 yrs ago, his daughter lives with us full time and sees her mom every other weekend. She treats me like crap, is fine with everyone else and then is all mad with me, I have never tried to take the place of mom, but should I stay or go, I am to the point I can't take her crap anymore, feel like i am under a microscope, and support both of them. Serious advice only please. My fiance and his x wife were divorced for 5 years when I met him and his daughter. Should i stay with the drama or leave?