Responses
It was the phone call, and the misconception of BOTH their feelings. Looking back at the phone call, Minjun had no context as to who the call could've been about, so I guess he only took in the key points rather than trying to figure who the main subject was (most likely some guy Jihwan was trying to shake off). Yeah but overall the plot could've been better if Minjun wasn't so insecure and asked Jihwan if he wanted to break up or not (which there was a 100% chance of him saying no to that ).
They didn't show what's the real cause of their break up wtf! Didn't it happen because of the phone call? what jihwan said in the present is different from what minjun remembered and they didn't even show the details about the phone call. Im unsatisfied with the plot.