Companies do forbid their talents from dating, but I think that's pretty much when they're fresh and new and being aggressively marketed for the first time.

With the short leash their companies have them on (apparently sometimes they even have their cellphones confiscated), dating doesn't even sound feasible, but I do believe these celebrities maintain private relationships that people on the Internet have turned into a science to figure out who is dating who or whatever.

Keep in mind, they are marketed to naive kids who fly off the handles when their pure and perfect idols turn out to be mortal. I think this is similar to the infamous cases in Japan of idols who are supposed to maintain a "devoted" relationship with their fans and whose fan bases EXPECT them to never have a relationship. I think it might be worse in Japan though with how much these talents have to appeal to otaku (don't think of the Americanized connotation for this word, these are the "waifu" people I'm talking about). There's different dynamics at play that I'm not very knowledgeable of, but I find all this shit fascinating af.

I have heard of K-idols openly dating. I think it's just a hierarchy, like you reach a certain point where your company will actually let you have a social life. It would be weird of them to treat an industry veteran like the company's freshman. I think the tough part is the initial stages of marketing a new group. You always here these celebrities talk about the earlier parts of their careers when they weren't even sleeping or eating (which is treated like totally normal).