It does sound like he is using again. And like the instant gratification he gets from the drugs he wants that same instant gratification from you.
I think confusion come from NOT living in reality, holding onto a fantasy then trying to make any little thing fit that fantasy because there really is nothing confusing about reality. Do we like the reality, of course not it’s so much less painful to grasp onto the fantasy and push all that pain away for another day.
The reality and facts are right in front of you he’s an opiate addict and he got a prescription for a whole month of codeine. He’s doing what active addicts do with crazy talk and behavior.
You can make the choice to block his # and be done with feeling perplexed and angry.
And then one day if he ever truly embraces recovery and decides he wants to talk to you as a mature adult, you can make that choice as well if you want to or not but right now he’s pulling you down that hole with him.