Actually I don't think Tidus went back to his own world.....his world faded away when the fayth stopped dreaming
He went to the farplane with braska, his father and Auron. But that's still not that sad cause at least it's supposed to be like heaven or something
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I think at the end when it showed him in the water and he was smiling and swimming up......maybe it was under the dock on the water where yuna whistled and somehow that allowed him to leave the farplane? I dunno I guess it lets you come up with your own answer.