He was imagining it & what their relationship could have been if only everything didn’t go the way it did. You can tell cuz Sungo doesn’t have a scar. Even if they really made plans when they were young (the flashback) obviously they never got to act on it. So Dohyun kind of did a “what if we did...” and imagined it ╥﹏╥
Back in chapter 66-67, our guy had a fantasy of 'what could have been if he hadn't been such a dick', where he and his man we're getting an apartment together and generally being a normal, cute couple. In this fantasy 'what it's world, as others have mentioned, Sungho doesn't have scars on his face. In this chapter, our guy was going back to that fantasy world to invision fulfilling that vacation they never got to take - I'm hoping we'll get to see the real version of them two going on it - probably much more awkward and less sexy, but much better since it'll be a real attempt to make amends.
Either way, every time this updates it's so awesome!! (๑•ㅂ•)و✧

wait can someoje explain this to me i'm so confubsed