I understand many of you (me included) aren't exactly fans of the... harem-esque route this series is going with these guys over Yoo-il, but I see it this way:
I think our main thread is with Moo-yi and Yoo-il because, it isn't "I'm this guy's fan... could I pursue it?" (i mean, Yoo-il wasn't a fan of Moo-yi at the start) as other series might go for, and we are seeing how their relationship is evolving from they were more strangers at first who shared a similar interest.
The thing with Ryu-min, I suppose it's more a cute crush Ryu-min has over Yoo-il and nothing more. That's why she reacts to it differently, because she knows she is a fan and there are some lines a fan shouldn't pass with their idol if they are getting closer to each other. I don't think for her, it's about "love" in a romantic way. I don't think this one could go further than that.
And the thing with the chef... Well... the chef is definitely sketchy. We don't know exactly what are his intentions, although there are some clues here and there that might be relating him to Moo-yi's stalker (or is he the stalker? we don't know yet. Could it be a red herring?)... so, why did he get close to Yoo-il in the first place?