Typically this sort of behavior is due to “come downs” so I wouldn’t be so quick to think he isn’t using. He may well not be but what id suggest in that case is to ask him if he’d agree to drug testing and do it weekly or every four days at least. When I did this I still got lied to even when the test was positive. Lying is ridiculous! I think they probably Believe their own lies – DENIAL!
If he is treating you this way when he isn’t using id be suspicious ad to why. On top of that I think you’ll always wonder and worry if he is using or not and that’s no way to live.
As for the Jekyll and Hyde, having a two-sided personality – one side of which is good and the other not so is all warning signs of drug use.