I've never heard of a doctor prescribing subs in a plastic baggie. You wanna know if he really has a prescription? Ask to see the bottle with his name on it... of course he won't show you. And there's your answer.
And if your boundary is that you won't date someone who takes prescription subs to stave off a heroin addiction (I wouldn't either) then the whole discussion is pointless anyway. You can't save him and make him work his recovery the way you feel is appropriate.
In order to move on and "continue your life", I think you are going to have to let go. Maybe that's what your are struggling with right now?
I'm not sure if checking my ex's bag was codependency or not. I didn't do it for him. I did it for me. My boundary is No Drugs In My House or Around My Son. He was behaving strangely. I suspected there were drugs in his bag. I checked. I found drugs. And then I kicked his butt out and I haven't spoken to him since.
It only would have been codependent, if I had begged him to stop using drugs and allowed him to stay.