Tidus is waiting on some criticism, maybe a shut up--so when he gets nothing but raw emotion enveloping, his complaints and readied defences slip away from his throat, anything he could have verbally expressed gone.

There's the nag of a comparison he doesn't want to make, that doesn't exist in any part of this. But his bottom lip twitches, the thought refusing to leave; and he holds onto Inigo tighter, realising his hypocrisy, what a bad friend he's been. Because he knows how easy it is for someone to disappear, to be gone, and they won't be back. He knows how desperately you want to hold them one last time, but--you can't. You won't.

But he wanted to avoid it, even when Inigo needed more than his reassurances.

He wants to apologise for it, for being a liar; but he knows better than to say anything, so instead-- Tidus hopes Inigo's story won't end the same as his did with Yuna. That Yuki will come back, and not leave behind the future waiting for him here.

That he'll be the one to comfort Inigo soon, like this, just as he had wanted to for Yuna when he was the one disappearing.