I wonder too, maybe there will be a secret Arne route or something, but that probably sounds weird.
Here are my guesses of what could be going on:
- Arne was originally a route but was scrapped/reused (considering Torulf and Arne are the only characters with sprites for harnesses, and the fact that many of the character sprites are still in the game files)
- Arne is actually meant to be a future route, but I highly doubt that, because that doesn't make any sense
- One other guess I got is that maybe Arne was having some sort of affair with Devon (considering they are colleagues, I guess and maybe of age?) but was switched later on.
Honestly I absolutely no idea.