I don't think it's that disappointing, actually, since it revealed that they were childhood friends together, all 3 of them. It makes Eun Hyuk's character make sense now. I didn't want it to be Eun Hyuk originally, since his behavior wouldn't make any sense if he was the one who slept with Yoo Jung. But now that I know his backstory, it works. And we also see him ignore a call from Yoo Jung, so he's committed more to Ji Wook than his (former?) crush, so... I mean, that's pretty fascinating for a second male lead!