It wasn't long ago that Byakuya and you were secretly seeing each other. None of you would have a problem making your relationship public, but the Togami family would. Tradition prohibits Byakuya from having a partner, but that didn't stop you both from seeing each other secretly when his family wasn't at home. Aside from that, Byakuya trusts his butler enough to know that he won't have any problem with you.

“I was thinking about what you said the other day.” he says with a calm tone, not even looking at you; he seemed more focused on looking at the stars from the balcony you were both on. “About your desire to get married. I'm glad you understood that it's not something we can do so easily—but still, I want to hear you. How would you like our wedding to be?” he asks, now looking at you.

He was probably cheesier than normal because it was 2 in the morning. Maybe you should take advantage of his state and tell him your desires without filters.