He wasn't exactly sure when he started feeling feelings for Tao. 

Was it when they first debuted? 

Or, was it before that even, when they were training together at SM?

Perhaps it was that time mid-2012 when he first held Tao in his arms. When they were all desperately missing their families, as they couldn't see them too often due to their rigorous training schedule. Tao was feeling the strain more than the other members; his overemotional tendancies paired with the fatigue of training definitely made him the first to crack. He sobbed as Kris held him in his arms until he finally fell asleep, promising that everything would be alright. 

Maybe he first fell in love when a semi-delerious Tao whispered to him, "As long as you're holding me, everything will be alright."

Maybe that was when he first felt the dreaded shock of electricity coursing through his body. When he first felt something for his friend.

If it was then that he fell for Tao, it was definitely these words that first taught him heartbreak:

"You're a great friend, Kris."

...

Whilst he wasn't able to pinpoint when he first fell for Tao, he could certainly say why he did.

Kris loved the confused look Tao had on his face whenever he was made fun of. 

The way that Tao looked to Kris to protect him from the so-called 'monsters' that came in the night after watching a horror film with the other members.