Found out boyfriend was smoking after I told him not to? HELP?

You are going to have to stop telling him what to do. You can express concern about his health, you can tell him that you disagree with smoking, but you cannot make him stop. It is his health, and you are not his mother. Talk to him honestly and gently and tell him that you are worried because of the health effects of smoking. Maybe he is just having a hard time quitting and he needs help, it is very addictive after all. Or maybe he's just not ready to quit. But, whatever the case is, the more you yell at him, the less open he's going to be about it. He probably feels like he has to lie and sneak around because you make such a big deal over it. So, just take a deep breath, relax, and ask him if he needs any help.