I feel like we havent resolved things?

If he told you he didn't want to talk about it anymore, maybe the issue really is over for him. If it was a problem that had to do with the two of you, I would say to try to talk about it more, but his problems with his stepdad really have nothing to do with you, so you can't really do much for him other than try to be supportive. Maybe just send him a text or write him a note that says that you're sorry for what happened and the way you acted and the conversation ended, but that you want him to know you're there for him if he ever wants to talk. That way he knows you care, but you are leaving the option open for him to talk if he wants to do that.