The moment between them was a string, pulled taunt near to the point of snapping. To much pressure, too much pull, and the connection between them would break in two. An instant of understanding, a single word to bring them closer, and instead it might have turned into something stronger. A bridge of connection instead of a noose made to hang one - or both of them.
In just one simple sentence, the string snapped. Not neatly; thin strands still held on stubbornly, refusing to allow for a clean cut that would remove the overwhelming and suffocating sensation of betrayal that the words left. But the core of their connection was gone from nothing more than one
simple sentence.
I'm not willing to share at the moment.
With everything that Vincent was asking of him, the faith and trust he felt that Cloud could put in his companions, to hear that there was a piece of him that he simply was not willing to share-- it made it feel hollow and empty. Little more than a lie meant to offer hope when none existed.
He wanted to find something pithy and cutting to say to underscore the moment, but Cloud had never been good at coming up with spur-of-the-moment comments. Perhaps it was better that he said nothing, leaving his response as little more than a long, empty stare.
The airship would stop before long, and when it did he would leave. Tifa would try to stop him if she was aware of what he was planning. Barrett would curse him... and it didn't matter. If the world was going to be saved, then he was not going to be part of it.
The one who helped to lead Aerith to her death did not deserve to save a world that he had condemned.