Sora is a very special person, Terra. He very easily opens his heart to others and, more often than not, hearts respond in kind. Ventus chose Sora's heart as a place to rest. They have a much stronger connection than you can know... Ventus himself said that Sora had given him a second chance...

[ she reaches over to tap on Terra's hand. to get his attention. to look at her. ]

I don't know what happened that night. What I do know is that Sora would have to find the place where Ventus physically sleeps to return his heart. I know that Sora would. He has returned a lost heart at the risk of losing his own before... But perhaps Ventus isn't ready to go back. Just like Sora is unknowingly there for him, he has protected Sora as well.