I ate the last two slices of pizza that I was supposed to save for my roommate
Why did you eat the last two slices?
That little swine ate my last slice of pizza last time.
That's really selfish. You should communicate with your roommate about problems that you are having. Talking about it will help prevent resentment from building.
If that asshole thinks he can run this place, then I'm better off on my own.
If you are that resentful of your roommate then I do suggest you leave. Maybe it's best not to live with someone you hate that much.