Shifters lie, all the time, to everyone in their lives. Small lies, big lies, all sorts of lies. And they have to, it's easy, it's essential, and it keeps them safe.
So for Emmett to be truthful, really wholly truthful with something so important as his heart, that's hard, harder than it is for us. He has a lot more to lose. Apart from Huan-Yu (and that was fluke), Jian is the only person Emmett's not related to he has ever been able to be honest with. He only has one person filling all his needs - Jian is friendship, adoration, lust, love, companionship, the guy he can laugh with, cook with, and talk with without lying constantly under the surface. To lose that would be the end of the world in Emmett's eyes - no wonder the boy is careful.