Claustrophobia

"You know, most boys would enjoy being trapped in close quarters with a girl." I roll my eyes.
"Not claustrophobic people, Tris!" He sounds desprate now. - Divergent, page 325

Four and Tris again
It's when she was in his fear landscape, where we find out one of his fears is confinement.
He makes me melt omg sdjhkjhgaksdgagh
(the anatomy really sucks so just ignore that, it was quick )

Tris and Tobias\ Four (c) Veronica Roth
art (c) Moi