Hurray for love confessions!
Too bad that also confirms there won't be a triad.
I mean I certainly wouldn't count on a poly ending the way things have been set up so far
BUT
There are a couple things to keep in mind.
First of all, the author was interested enough in the idea of a threesome to draw at least a couple pictures of it. If the idea were off the table on some basis of ethics or aversion/squick we definitely wouldn't be getting a couple panels depicting it!
Second of all, I'm not convinced we're supposed to take Jun's argument about the distinction between idolization and love uncritically. If anything it's almost the opposite, that idol cutlure tries to market itself in a way that breaks down a distinction between person and product, to try to turn that sort of possessive feeling into acts of consumption. The whole thing about parasocial relationships, that's what they're talking about. Hence why you get people feeling betrayed when an idol gets revealed to be in a relationship, why you get people who do creepy stalker stuff, and why you see people who vandalize their own possessions related to an idol when personal information gets out in public.
Given that Jun is very, very into that idol culture and also very, very single I think it's reasonable to say the story doesn't want us to take Jun's argument without a grain of salt. I certainly don't agree with it!