This is no misunderstanding. When I was 13-14 I had a similar experience. My step mom was a horrible person, on many levels. I was supposed to do the weekly switch as well, and I got to the point of finding any reason not to go to their house. Stay at friends, lie and stay at my mom's, whatever I could do.

I am nearly 38 years old. And this still affects me today.

The best thing you can do, is speak your feelings. Get it all out there. Parents are blind to a lot of what kids feel, because kids often have trouble expressing their true emotion and feelings.

Eventually, you will be more powerful than your step-dad.

Don't think, "oh no I ruined my mom's happiness". If he treats the woman's children he supposedly loves the way you say. It might be far worse for her. You telling her what happened, and how you feel might be what she needs to take the blinders off.

Be intelligent, strong, and don't be afraid to do what you need to.