I'm not saying he's going to cheat again, I'm just saying he doesn't get why it's so important to resolve rather than avoid this stuff.
He is an adult and can do what he wants. I think some communication to clarify that you are afraid of having less quality time with him if the tobacco use affects him in causing oral or throat cancer, but that you can stay with a tobacco user (if that is true), but not a liar, might be helpful.
I also don't know how to help him.
Nothing for you to help him with. Tobacco use and lying are both his choices.
I agree - the lying is a potentially big problem. You've already resolved so many issues - you can resolve this one, too.
He says that he lied b/c he didn't want me to know that he had slipped up. I'd rather him be honest and it disappoint me, than to be lied to it and it break my trust again.