"Then I'll regret if you don't dance!"

He has to speak loudly with the noise and energy around then, but Tidus looks far from displeased. Their hands stay linked, better so when Tidus can fit her hand better into his, guiding her, "Reach out!", and if she's been watching the dancing, she'll know he means to join hands with another person.

But likely, somebody will already be reaching to take Nell's hand to connect her to their circle.