He won't, he'll stay to only leave for the endings. This is kind of a similar result as the full share route ending, where Mc and Andrian both leave and visit the house on holidays and events.
Do you know if we will at least get a different route for enabling the trip to Japan without sharing any girl with him? Like a different way of befriending him? maybe through some mini games? Like teaching him how to drive since he seems to have once broke Josef's car judging by how Josef asks you to not let Adrian drive
That would be awesome to get at least a different way of befriending him without sharing anyone