I really can't stand my dad's girlfriend?

So, ever since I was about 4, my dad cheated on my mom with his now-girlfriend. When I was in 5th grade, my parents got divorced and about a year later my dad finally moved out of his apartment. Of course, his mistress moved in too but he never asked me about it. It has been 4 years, and at first she was really nice, but within the last year, she has begun insulting my mom and yelling at me nonstop for things like accidentally leaving my ceiling fan on. She tells me that my mom is jealous even though my mom has a boyfriend. She says my personality is terrible and that her sister has no respect for me and all these things, and then she makes it look like she was the innocent one. I have had to leave and go to my mom's before because of what his girlfriend said to me. She is about 6 months pregnant now, and I can't stand her. I don't even like my dad, but I have been able to put up with him to see his girlfriend and everything. Now I just want to live at my mom's and not come here, but both my parents act as if they don't have a child and make plans without consulting each other, like if there was an emergency I wouldn't be able to go to my mom's because she is an hour away with her boyfriend and refuses to pick me up. Out of the two parents, my mom is without a doubt my favorite, and I just want to get out of my dad's house. Is there anything I can do? Please help, all this really stresses me out and my grades have dropped dramatically because of it.