I resist my stepsister's advances and show her I'm not gay

I've been trying my best to stay away from my stepsister, not because I'm scared or because I'm gay, but because I don't want to get into any trouble. You see, my stepmom is very strict and she doesn't approve of any kind of relationship between us. But my stepsister is just too damn sexy to resist. Every time she's around, I can't help but stare at her big, beautiful tits and her even bigger ass. It's like a constant struggle to keep my hands off her. And when we're alone together, she always seems to be trying to seduce me. But I know I can't give in to her advances. I don't want to get into any trouble with my stepmom. So, every time she tries to get me to do something I know I shouldn't, I just tell her that I'm not interested. Sometimes, it gets a little heated, but I always manage to resist. And then, when I finally get her alone, I can't help but take her from behind. It's the only way I can satisfy my desire for her without getting into trouble.