Man don't wait fro him to catch you. Then he'll think that you're not as open with him. He'd probably definitely rather have you tell him openly then him find you sneaking around smoking and shit. Don't take the advice of letting him catch you. Just bring it up in casual conversation. Maybe don't even tell him that you do but something like you are thinking about trying it. See how it goes. If he says no I don't want you trying it then I guess keep it secret but if not then you can go from there. Maybe he'll say well if you're going to the I want you to do it with me.