What do I do?

Alright so this guy and I kind of have an agreement where we don't fuck anyone else but each other, and he really likes the idea of me being 'his little slut' which is cool with me btw, but he's a really big asshole. Like he never asks what I want and just kind of orders me around. Like to send nudes and sext him and today he literally was like 'I'm counting on you to keep me entertained' and got mad when I had to do something for school and couldn't text him back right away. It's really frustrating because it feels like I don't have a say, but we never discussed having this sort of relationship. So what do I do? I don't mind the d/s thing but sometimes it feels like he's not treating me like I'm a human being. You know?