Balthazar, at least, doesn't have to worry about shock or disapproval from other angels. He's already earned their disapproval. If they run into him, most of them, they'll kill him before asking about his sexual history. Castiel might notice something, but he doesn't ask many questions about Balthazar's private doings, either.

The greatest danger to Balthazar here is from himself, ultimately, and the second-greatest from Lucifer. He's too wild with affection, and too sex-addled, to fully comprehend the risk Lucifer himself is taking, but through the link between their celestial selves, he can sense, dimly, that he feels Balthazar is...worth something. Special. He's never been special before, to anyone. There's probably some kind of sin in how alluring he finds that feeling. Pride? Envy? Ehh, fuck it, one transgression at a time.

He's not clear on the full translation of the murmuring. Angels can know any human language, but not necessarily all of them at once, and this is not quite like an earthly tongue, but he recognizes the word for butterfly, interprets it as a pet name, and his Grace all but sings with joy. Giving affection is easy. Being offered it is utterly irresistible.

This is crazy, this is madness, he's known this Lucifer for only a few hours. He doesn't care. Every motion of their bodies sends him higher. His own endearments are gasps in Enochian my heart, my jewel, my treasure. They don't have to pace themselves, they don't have to hold back to wait for the other to come to climax with them. They're so closely linked now it's inevitable that one will follow the other, although whose pleasure is leading and whose is following is hard to say.

"Lucifer, yes," his vessel is breathless, the gasp almost inaudible, but the sentiment since through his Grace.