why does the narrator decide not to enlist in the army with Binker?

Gene basically wants to be near Finny. Gene realizes that he doesn't owe anything to either Devon or to his parents anymore; the choice of whether or not to go to war depends on his own inclinations, and he wants to go through with it. But, then he goes back to his room, and finds Finny there; suddenly, what he resolved to do no longer matters, as he has a purpose to stay at Devon again.