I recently expressed my interest in a poly relationship (specifically a triad) and he kinda flipped out. He called me a slut and punched a hole in the inside door of our car. We haven't really spoke of it since, and I'm not sure what to do. He keeps making pokes at me about it trying to make me feel bad.
This is not an issue of polyamory - this is an issue of abuse. A man who calls you names, damages property to demonstrate his anger, and insults you to try and make you feel bad is not a safe or healthy man. This is not your fault for bringing up a conversational topic he didn't like. This is his fault. He is being dangerous and cruel and you need to leave this relationship.
Check out my resources here. And good luck. You don't deserve to be treated like this.