What if he went mad exactly because of Y? What if Y exploited his desires so Qin Xian would travel from world to world to collect the energy? (⊙…⊙ )
Might be a possibility...but it might also not have been intentional.
MC falls unloved with system and system doesn't understand human emotions and continues to reject MC can drive a person crazy in MC's situation as the only constant he has throughout those worlds is Y and he desires love and companionship.
Seems more tge makings of creating a yandere than being in purpose. But it doesn't mean Y didn't use it to his advantage and made a deal with MC.
After all, Y became Wang Yi and X was very happy about that. Still ate him though so he could never lose him again.
I think maybe Qin Xian was in on it, after all he went mad with desire for Y and challenged the System himself.
Even as X he was continuing his own desires as he ATE Wang Yi to fully tie them together.