I Want to Love Like You

When Zhe Chouhen woke up, he found that Daoist Panda was no longer by his side. 

He went to search for him, but heard a voice in his head. 

[Don't come near me. Something wrong is going on. Wait there, let me look for Stein.] 

Zhe Chouhen became worried. (Something wrong? What is it?)

[I'm not sure, but I have a feeling. If we want to continue with the plan to make me the male lead, we need to ensure it first. Today is the day Stein learns about everything about the last body owners, and this very moment can determine the ending. I need to be the one who's there for him.]

It makes perfect sense. But why....

Why does Zhe Chouhen feel an ache in his heart at the thought of Daoist Panda ending up with Stein?

Who exactly does his heart ache for?