From bliss' translation:
Xie Xiaofeng suddenly grabbed him by the shoulder and said, "It's you! You've come as well!"
"Yes, it's me. I've been here for some time, but I still don't understand."
That person turned towards Yan Shisan's body and said, "You should've known that I would've wanted to see him one last time."
"I know, of course I know."
He had never forgotten what Tie Kaicheng had said either.
He had no friends and no family, although he taught me his swordsmanship, he never allowed me to befriend him. Nor did he ever let me know where he came from or where he would go.
Because he was afraid of having sentiments towards another person. Because if a person wanted to become a swordsman, he couldn't have any sentiments.
Only Xie Xiaofeng knew that the comradery between the two of them really did exist, because he knew that Yan Shisan wasn't really emotionless.
"If he had really struck out, then my life would've been forfeited. But even until the very end, he never struck out."
"Because he didn't have the intention to kill!"
"Because he had saved my life before!" Xie Xiaofeng knew Tie Kaicheng wouldn't understand so he continued, "If you've saved a person's life, it will be very hard for you to take that life back. Because you will already have developed a level of sentiment between the two of you."
This was indeed a very difficult sentiment to explain. Only humans are capable of developing this kind of sentiment. But it is because humans have this sentiment that they are human.
What kind of sentiment do you think Yan 13 developed? Could it be... some kind of love?
Furthermore, could Tie Kaicheng have developed a forbidden type of love relationship with Yan 13, one that was not allowed to be explored (perhaps b/c Yan 13 was afraid of having feelings)? I base this on the way things were worded: Tie Kaicheng said he wanted to see Yan 13 "one last time." In my personal experience, that usually happens when you have some kind of romantic feeling for the other person (whether you realize it or not).
Now, I realize this may be completely not what the author had intended. However, using my own feelings, when I read that passage, I really got the impression that Yan 13 had developed a love for Xie Xiaofeng, and that Yan 13 was trying very hard to subdue his emotions, but in fact the more he restrains, the more complex the feelings become.