There's a fine line between pushing a story too hard and making it believable enough, and Steph is unsure which side she's on right now, "It isn't. I don't know how to convince him to break it off before mom finds out."

She wonders idly how her mom would have reacted if Arthur had ever cheated on her, but that would've required being conscious of her surroundings.

"I think it might be best to leave it for tonight," because it's not just the risk of getting caught by a hypothetical mistress. If Steph gets caught by someone with ties to the militia, she might not ever come back, "But shouldn't I be offering you a drink? I did interrupt your evening, after all."

Now that she isn't focused on the other woman, she's starting to pay attention to Irene, and she seems familiar. Although Steph can't place her, she's curious enough to want to stay.