Riku couldn't lie to himself... he was kind of disappointed that they wouldn't be able to celebrate his birthday in some capacity. It was the first birthday in so many years that he'd actually be able to mark. To not celebrate it at all... it made him kind of sad. But, he needed to do what was right for the Prince. Which meant putting his arms around the Prince, kissing the side of his neck, and reassuring him, "Don't worry about it, Sora. I've waited this long to know a birthday, another year won't hurt. This year I actually know when it is, and that's quite a lot."
He untangled himself from the Prince when there was a knock on the door and went to retrieve their tray.
"Sugar, Sora?" Riku asked, pouring the Prince a cup of tea promptly.