Damnit.. I got so confused.

He got Hyoun's orb so it's either they become eternal mates (he accepts the orb) or Taehyuk dies. (He rejects the orb) The river is called Sanzu, and it's the one that takes you to the afterworld.

Ty. But I was confused in the beginning where he wanted to check his head. But after the whole Styx thing I realized what was happening. He's dying