Simon does not yet know about this rifle. Once the news is broken to him, he will, of course, wish Kaylee and her new beau well, and retain only the politest interactions. He'll also quietly wish horrifically painful boils in private places on the man. (Sorry, Dean; it's nothing personal.) And yes, boys are dumb. Which is why River is never allowed to have one of her own.

"Shhh, shhh, mei mei." He's trying to comfort her, already wondering if he can beg, borrow, or steal a sedative so she can get obviously well-needed sleep while he slips away to rifle through the drawers in Serenity's med-bay. "All right, we can fortify."

It's a good thing where River is concerned, Simon has unlimited patience.