My boyfriend is secretly smoking...what do I do?

Well, that is a very difficult situation to handle, but I think you should wait about 1 week or so and if he is still smoking, then calmly ask him to be honest with you and tell you the truth to if he is smoking or not. If he lies to you, then he'll lose your trust a little. Tell him that you won't get angry if he is smoking and that you'll both discuss your points of views and sort something out between both of you.