"Seonwoo" that we all saw throughout the manhwa is the GAME version of Seonwoo. (Real world/OG) Seonwoo had long returned to his own world. They both switched places long ago, with "OG Seonwoo" coming into the game world while "Game Seonwoo" take his place in real world.
Then at the start of the manhwa, we saw that Seonwoo got transported into the game world, because this is his original world.
For those that doesn't understand:
First error (Bug) - 1st switch
Real Seonwoo --> Game World
Game Seonwoo --> Real World
Then the world system correct itself at the start of the manhwa, switching their places once more.
Causality>>Correction - 2nd Switch
Game Seonwoo --> Game World
Real Seonwoo --> Real World
The "Yeon Seonwoo" that we all saw from the start was always the "Game Seonwoo".
So when Jaehee rewind time, "Game Seonwoo" woke up at the start of the manhwa, meaning Jaehee will meet the same "Game Yeon Seonwoo" that he fall in love with.
That’s so random, tbh it doesn’t really change anything in the plot, beside the fact he doesn’t have to go back to real world, cause it’s not his ‘real’ world, lol. Anyway I hate the ending it’s so freaking rushed, suddenly everyone is bawling their eyes out even though they were pretty much emotionless throughout the whole story. Wayyyyy too rushed author-nim. Receive my wholehearted hate, I loved this story, like let’s be real wtf is this ヽ(`Д´)ノ

I don't understand. Did he go back to the first time he woke up in that world, or did he go back to his world?