In a few chapters the status screen will say that the reward for failing the mision is going back to his world but there are many rewards for stay after finish the mision successfully and the choice of going back BUT if he choose going back, the people he saved will die (like the mother and brother of Alexis). So HE CAN'T GOING BACK ╥﹏╥
After the final battle, our Mc (Yuujin) meets the real Eugene because he took his place in his world and he's actually enjoying having a loving family, so the two of them are OK.
It's bittersweet, in the novel Yuujin cries sometimes because he miss his family.
I don't like this couple because the story is going to be so rushed that it won't make any sense. Plus, they haven't appeared much in the main story, and I really don't connect with them; what little I've seen has been frustrating. Good for those who like them, but I wanted to see more of Byul and Siwoo because I feel like their story still needs more development.