Basically There’s 2 seonwoo’s
Game world seonwoo and real world seonwoo
-Real world seonwoo got sucked into the game as a kid
-Game world seonwoo switched places with him and went to the real world
Game seonwoo (that now is living in the real world) forgot his memories and continued living his life thinking he was actually real world seonwoo and he’s the MC we’ve been following the whole story and we see get sucked into the game (again) by the even of first chapter and last chapter here
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Now when seonwoo sacrificed himself and jaehee rewinded time again the game fixed the glitch and we thought seonwoo would go back to the real world because viewers and seonwoo himself thought he was real world seonwoo….but no real world seonwoo (the one who got sucked into the game as kidd) managed to return and and seonwoo (who we thought was real world seonwoo but in fact is game seonwoo) was in limbo because he died until jaehee reversed time and that’s the last scene of last chapter where he wakes up confused in his bed in the game world thinking he got sucked again (the event of ch1)
I hope this makes sense

I don't understand the ending can someone explain me please ( ̄へ ̄)