I don't like my stepdad & I don't know how to cope.

I'm 16. My stepdad has been with my mom for about a year. He hit her in the beginning of their relationship. I told him He had to ask me for forgiveness as well because I'm her daughter & that's disrespectful to her as well as to me. He never apologized. He's always serious. Always mad. He cheated on my mom probably 2 times already & not so long ago that my mom catfished him & he agreed to meet up. It seems that he only cares about himself.

So today, we're back to school shopping & we wanted to go to Academy while he wanted to go to Sears to buy tools. We literally passed right by academy & he said we'll go on the way back. It pissed me off but I was like, ok, at least we're going. Then, on the way to sears I told my mom I wanted Starbucks (which is inside the mall by sears) & she said no, so I said "please?" & he told me to stop acting like a little girl & grow up ??? Like wtf. How am I acting like a little girl simply by asking for Starbucks?