I’ve perfected the art of the fake smile. It’s not so difficult when you are completely numb.

you're always smiling and it seems so friendly, but the way you smile is so empty, it hurts just to watch.

Numbing the pain for a while will make it worse when you finally feel it. (Dumbledore)

Just because you don't want to see something doesn't mean that it will go away. Do you think inhumanity doesn't exist if you pretend not to see it? Or maybe get too drunk to understand? We've forgotten the things that make life worthwhile.

You have to remember that there are reasons to live, and that at least a few people are decent, and that the world is worthwhile some of the time, okay?”
I raise my face to his, wanting another kiss, but he stops me.
“You will remember?”
The balloon bumps downward again. His eyes are still closed.
“Why don’t you open your eyes?”
He opens one and squints at me for a second. “I’m terrified of heights,” he says.

So you try to fake a smile and it'll probably work for the first time, But till when could it cover all the pain that you hide inside?