Responses
EDIT: Rather than hanging up, they just said their goodbyes too quickly- with Eunpa wanting to get over the phone call quickly so he timed it so well that his hyung is still at work. The fact that he didn't want to wait for later to have a longer conversation with Eunsan suggests he's doing his best to avoid giving to many details about something he's just thought of as an excuse.
For me, that quick goodbye was hiding something but in such a subtle way that even Eunsan won't suspect a thing.
The fact that Eunpa has that "oh god, do I really have to?" look on his face while telling his hyung that he's s NOT gonna be home that night is just telling. He didn't even bother to explain and reassure Eunsan that he's gonna be okay even when in the previous episodes, we know how sensitive he is to his hyung's over-protective nature and in fact, both seem clingy and devoted to each other as siblings. Hanging up while Eunsan was still asking questions is just...OOC on Eunpa's part.
So I guess he GOT the feeling that Ian's gonna monopolize Eunsan again (I'm sure he's caught on as Ian has been spending the weekends with his hyung even when they're already together as workmates) and as he seems a smart kid, he knows who Ian likes... and it's NOT him.
Eunpa's heart must be conflicted... as he seems to have a bigger crush on Ian than he lets on.