Throughout his life, Troy has been whatever everyone else has wanted him to be. A football player, prom king, the Chosen One of the plumbers. Even with Abed he was participating in Abed’s interests and fantasies. Don’t get me wrong, he I think he genuinely enjoys those more, but it is just following whatever someone else wants for him.

Throughout the show, Troy has slowly learned to pursue his own interests, inspired by Abed’s confidence in himself, despite society alienating him. Abed being himself and being comfortable with that slowly allowed Troy to become himself as well. But, he is still heavily attached, even codependent, on someone else.

Seeing the world gives him a chance to forge his own path (literally?? Guess there aren’t any paths in the water but still ??) and come into his own. When he came back, Troy would have become a separate entity with Abed, rather than just an extension of him.