He doesn't know what to do and he is certainly panicking. Lan Wangji is going to kill him if he finds out. "Ahh...I'm sorry. I'm very sorry."

Flirting will be the death of him yet..he needs to learn to turn it off. Normally he could probably take something like this in stride and perhaps even falling into a teasing way with it but the fact that he already has an engagement to an extremely jealous and possessive individual makes this a bit harder to handle.

"I am sure I wouldn't be a very good husband for you."