He'd just tell you if you couldn't know something. They have a lot of secrets.

[That Kanda probably knows too many of, because, as Aerith said, he's known Lavi for years now. Belatedly, he realizes he didn't know if the marriage thing was a secret. Oh well.]

He'd ask you about yours back, though. [In case that's a sore spot for her, though he doubts she'd have a problem telling Lavi "no" in return.]