Mary Jane

My boyfriend has always smoked weed, and he knows I hate it (to an extent) and sometimes I catch him lying about it. When I ask him, he admits that he lied but why is weed such a "big deal" that people have to lie about it. He did it before I met him so I can't change him, but it worries me that he's going to get in trouble. It's not that I hate it, I just think it's an annoying "drug". What should I do?