Against his will, he was pulled away from talking to Sora and his strange new friends. He was about to break free from Maleficent's grip when she whispered, "Watch Sora's reaction to your disappearance, Riku."
He didn't want to disappear but he was curious about it, because deep down something hurt from seeing Sora with new friends.
Right before his eyes he watched as Sora looked around for him, and then gave up his search to walk away with those friends. Something like pain pierced his heart at the sight. Didn't Sora care more than that?
His feelings were exemplified by the voice in his ear, telling him how Sora found a replacement for him… that he was expendable in Sora's eyes. Unbidden tears stung from behind his eyes. He had been looking for Sora; he realized on his journey that the only thing he truly wanted was to be reunited with Sora again, and he found other people?
Jealousy, anger and pain flared up in him all at once, and he glared at Sora's direction. A lone tear fell down his cheek as he turned to Maleficent. If he wasn't worthy of Sora, then Sora wasn't worthy of him.