Sora tried really hard not to turn pink. He rarely had someone acknowledge his and Riku's relationship like that and it felt really good and a little embarrassing. It was especially nice coming from Corin, who came into this in the middle, when Riku's situation looked so suspicious, and he didn't know the kind of person that Sora was.
"Listen," he said, scooting a tiny bit closer. "I do not wish to take him from you. I want you to spend a lot of time together while you are here in Hollow Bastion." Because otherwise when were they going to see each other? Once a year if Riku was lucky? "And I apologize in advance, but simply being the brother of a man the Prince is courting does put you on the spot. I only ask you to be careful with what you say." Sora KNEW that Corin was smart. He could figure out, no telling everyone that Riku was a servant. No telling everyone he was common, or stolen from home, or didn't know how to read. No telling people that they were engaged or even IN a relationship.
The Prince got up and held out his hand for Corin to take as a gesture of friendship. "And you must know that if you ever need anything you can come to me or Riku directly." If he ever felt overwhelmed, needed help, didn't know what to say, he could defer to the Prince and that was okay. Sora could deal with anything.