Step Dad and Step Sister?

Okay so, my mom is getting remarried soon, and honestly.. I don't like him, i'm 17 and going to be 18 here in December. I know that i shouldn't worry about my mom's life because i'm almost out of the house anyway. But while i'm still here my moms fiance if you will puts me down for every little thing. I could do everything right and still do it completely wrong, i could say the sky is blue and he would say no its blue and white, even though i wasn't including the clouds. His daughter on the other hand can do the same things that i do and its the most amazing task or thing she could ever do. shes 24 knocked up and has a one year old as well, her and her boy friend fight constantly but y'know she's little miss perfect. At times my moms fiance will snap with anger, he never hits though. If your wondering about my biological father him and my mom separated, and he only talks to my 21 year old brother. I just i don't know what i should do about all this i mean i had NO self esteem as it is and look at me know. i bust my butt doing everything for this man and he doesn't show a inch of respect for me, or the things i do. But yet respects his daughter that doesn't respect him and brings drama a whole bunch to our household. I just feel i can't do this anymore.