Other people have offered a better explanation, but this is what I got from google and my own interpretation, so it won't be an accurate translation and you might disagree which will help build a more correct viewpoint.
(First scene, Jiwon in bed having a flashback/nightmare)
- Jiwon) I'm home
- Jiwon)..... ?
- Brother) Oh you're back. I'm going out now.
- Brother) Ah! Say hello
- Brother) This is my friend xxxx (the name is deliberately blurred)
- Jiwon's thoughts) I still regret it. If I could revisit that day, I never would have looked at him. I was young and foolish that day.
- Jiwon) I love you. I love you (to his ex in bed)
- Jiwon's thoughts after seeing his ex cheat) How can this be!
- Jiwon to his ex) How! How long.... How long hyung... Was it a lie, that you loved me...?
- Ex) You loser. Did you believe that? Were you that naive?!
- Jiwon) Don't laugh. Don't laugh!!!!!
The next scene with DG isn't as clear in google (setting living room with DG and Jiwon), but Jiwon basically says great it's only a dream, why does he still have to remember his ex. That his head hurts, and he remembers having to drink with his professor. He sees DG asleep on his couch, them has flashbacks to everything that happened. DG says something like hello Sunbae, you weren't well so I was waiting here until you were okay or something. Then starts to make some small talk about exams, as he too is remembering all that happened earlier. Jiwon has a flashback to his ex's face and is motivated to have courage to just ask DG straight "I was wondering if you love me" DG gets flustered, so Jiwon asks him again, and DG says yes.
Well from what it seems, by looking at the next chapters. Jiwon gets a hint that DG might think he is in love, but Jiwon doesn't think DG is being sincere, and Jiwon is Mr coward so he shuts him down in the next chapter and says if DG loves him, and he wants something more from him, then he's going to be disappointed and that Jiwon will find someone else to sleep with. This, we now know, came AFTER Dong-gyun heard Jiwon crying about a "hyung" in his sleep and saw the crumpled up photo of Jiwon's graduation. Chanwoo has a bit of a pep talk with DG in the latest chapter, saying the guy he's seeing must have been hurt, if he is behaving like this and that DG should do what makes him happy primarily. DG then says something about probably never being able to reach Jiwon. I think it might take DG to be the more head strong character to make progress with their relationship, confront Jiwon etc as Jiwon is a bit stuck. The two are going to end up together anyway, such is yaoilogic (⌒▽⌒)

Why do I have a feeling that this is the calm before the storm? I don't know but I'm sure drunk alex will fuck it up in some way, like calling his exboyfriend's name or something similar. They have been showing alex thinking about his ex a lot though ( ̄ε(# ̄)Σ