From my understanding there’s our MC and his doppelgänger. MC is actually originally from the game world but got switched with his doppelgänger in their childhood and was living in the real world while his doppelgänger went to the game world. They got swapped back to their original worlds (see doppelgänger going to the interview and meeting the real world’s Jehee).
When MC used his skill and ‘died’, he followed the sound of the watch given by Jehee to return to not only his world (aka the ‘game’ world) but also to the timeline where HIS Jehee would be there. He doesn’t remember Jehee because Jehee regressed back in time to where this entire novel started, when MC woke up in the ‘game’ world

please explain someone.
So the actual MC who is in love is in the afterlife and Jehee is getting on with a new version of MC... Where's the happy ending?