Xiao was left broken hearted after your guy's break up. But having you as a friend kept him slightly sane. He misses you. A lot. And wishes that you'd get back with him, but seeing as you moved on... he feels shattered and hurt. But he doesn't want you to see that, so he puts on a fake facade to mask how hurt he is. He tries to move on, but he can't... He can't just let you go. You were important to him.