That is not the sunwoo we know that woke up, it's the one he had switch places with. We are seeing what happened while the story with the MC was taking place. The sunwoo we know is observing the other sunwoo ( like a ghost) That Sunwoo wakes up confused and realized he is back in his own world, and calls his parents. That's right, our MC and him had switched placed as children, but our MC forgot thinking that world was only a game (probably due to trauma) The next couple of chapters follows the other sunwoo meeting his parents, quiting his job and applying to a new job where he runs into this worlds Jehee who is the CEO and also who the gsme characte was based off of. Then seeing all of this, our MC realizes it would be incredibly selfish of him to want to go back to this world, after he realized he robbed the other sunwoo of his parents/life all these years. He is in like an empty space and is walking trying to find his way back to Jehee. The watch that Jehee gave him leads him to a light and then he wakes up lke in the beginning of the story, exactly the same with no memories. Except this time, Jehee rings the door bell and sunwoo is greeted with a boquet of flowers and the ML tells him he regressed and was his lover. 

First off side stories are r19

ML follows MC around and even reverses their contract so he's the slave and MC is the master. ML also lies that they slept together and they were in love with each other (not a lie, but did exaggerate). MC finds all of this hard to believe but thinks ML is so kind/gentle (Lol) Eventually he starts working at the guild again, and reenters a dungeon with ML/crew. That's where he reunites with bundles who cries clinging to him and is sad that only ML remembers him, so bundles gives MC his memories back through a memory orb that MC had in the first timeline. MC getd his memory back tells ML he has no shame pretending he's a green flag when he's a red flag. ML and MC reunite with intimate moment (not all the way but get each other off). MC immediately wants to prevent the ML's mother figure's death so they go meet her. ML eventually uses MC's memory orb to return all of the friends memories (because MC was sad about it) and they rewrite the future so no one dies and make bundles into a celebrity. MC/ML also do the deed at some point. There is one more side story where ML has amnesia and it takes place a few years after, showing everyone living happily (well aside from thr amnesia)