Early Tang Dynasty, Prince

Is he the King of Qin? Is he the prince? Am I Xiao Shuyou? Then who is Ouyang Ya! But when you wake up from the dream, everything becomes different? Is it Zhuang Zhou dreaming of a butterfly or Zhuang Zhou dreaming of a butterfly... If they switched identities... So in the end... Who is it and who is killed... So in the end... Who is it and who does he fall in love with...