The way I see it, he’s had the cute crush on his hyung for a while now and just realized the feelings are mutual. Then after sleeping with him for the first time hyung starts being rude and leaves Geonwoo to believe that he has feelings for someone else. I’d feel incredibly hurt and cry if I were in a similar situation. He just looks more like a baby doing it.
The way how I see it, each person enters a relationship carrying any sort of historical baggage. Any mature person should know that of their partner isn't comfortable with blurting everything out at the very start of a relationship, then it is best to bring up the question sooner but not right now.
From how I see Geonwoo's reaction, he is somewhat copying what Youjin (from another manhwa of the same name) was doing. Demanding answers at the wrong time and definitely in the wrong way. Unfortunately, this time the hyung is a lot less patient and understanding.
but remember this is his very first relationship... so the feeling of betrayal is very disheartening
For goodness sake Geonwoo, aren't you being too sensitive about this? Sure, your hyung is being an ass and not answering the question in a straightforward manner, but resorting to running away or getting dramatically upset is not a good way to react. You're kinda reinforcing your child-like demeanor....if you want answers, stand your ground!