Tidus isn't sure if Inigo means give up in a bow-chika wow wow way or to give into dating him entirely, but he can go with either regardless. How can he do otherwise when Inigo is reacting the way he is? He can be so goofy sometimes. Tidus loves it (especially when Taiki isn't around to get upset with him).

"C'mon, man, I thought you'd be the one guy supportive of us! You should be happy! I wouldn't do anything wrong to your sister!"

He's never done this before, really--but then, he's never meant anyone quite like Inigo before, who gets lost in his defences and puts himself in situations like these. Tidus isn't even sure he can take the credit for this. This is all Inigo.

But he will absolutely go along for the ride, sounding as close to hurt as he can. ...while still wearing a smile.