Oh, is there a twitch to Tidus's mouth at things to look forward to; there and then gone, but who knows for how long. He's certainly got something on his mind to mention, and he wasn't sure how to do so, to frame it, but in that polite questioning back:

"Alright! But I'm not the guy going and getting engaged, so who's the one having a better time out of the two of us?"

Yeah, like he was going to keep quiet about that. Senku didn't tell him to be quiet, and the way he dropped it was so mundane, that Tidus is glad for this opportunity now, to mention it at all, and ask with an eager curiosity: "For real, I didn't miss this happening months ago, did I? This is a recent thing."

Right? Right?? Please tell him this was a recent thing that didn't just happen to go over his head for ages.