Riku could always be positive about the Prince - he had a much harder time being positive about himself, or really about anything having to do with his family. And, well, old habits die hard.
Which was why he was NOT pleased that the Prince wasn't allowing him to stay outside, as he wished.
But, he was not about to push Sora's hand away, or deny him his turn to be helpful, loving, and caring. So he reluctantly met the Prince's beautiful eyes, and gave a slow nod. Fine. If Sora insisted.
He was still going to drag his feet a little as they entered the room. He sat down, got up again, and then made himself sit down once more because he highly doubted Sora wanted him wandering around the room while they tried to read.