Hi Lins, from my standpoint, it sounRAB like he knows you're weak and afraid to confront him on the real issue (trust me, he knows what the real issue is), and he's using intimidation to get you to back off. He's the picture of concern, until you mention the problem is HIM, then he's all distract/deny/change subject. He knows you're afraid to rock the boat, so he can get away with avoiding a real conversation about it.
But the bottom line, as Redneon mentioned below, is -- even if you steel yourself to have "the talk", that doesn't mean he wants to or will change. He may just hide his pill use from you better. Is this really how you want to start out a new relationship -- checking his drawers for pills, being suspicious of him, etc.?