I'm not quite sure what your deal is but that is an accurate description of the requirements to join the three-person relationship vs not. DPC's official walkthrough covers it, and I've played both DIK and CHICK characters, and my heavily DIK affinity character was not accepted even though he met the other requirements. Sex with Josy or the near-sex attempt with Maya and neutral or Chick affinity (not status, but major choice affinity) do the job.Is it even worth trying to argue with him at this point? He puts Maya and Josy's relationship on a pedestal and protects it tooth and claw and refuses to believe anyone claiming they have feelings for MC.
It has nothing to do with affinities or choices. That's just something he firmly believes for some reason.
I have no idea what his deal is.
Now, it may be possible in the future to re-initiate a relationship with one or both despite not being able to rejoin them at that particular juncture, but his statement's accurate, and it has nothing to do with putting 'their relationship' on a pedestal. Clearly that choice does not mean any existing sexual interest between MC and either girl is gone, and a plotline where the relationship between the two of them doesn't survive seems completely reasonable as a potential future development.