It's probably a fanfiction story but it was a story about the MC, he's an idol and he was dating IU but the MC still likes someone else from twice. I forgot the title but it was a good read. Also, if you have something like idol system to suggest. Please suggest, I'm craving for more idol/showbiz novel.
I highly recommend Top Management. Not really a system but the MC has power to see the future. Just to warn you though, the author abandoned the novel at around chapter 200. But it was a very good read. Learned lots about the K-pop industry.