Biting her lip, she's worried that she's pushed too far and gone into territory that isn't hers to discuss. Judging by his reaction, she thinks there are two possible explanations: either he's poly, as is his sub; or, this girlfriend simply doesn't exist.

She hopes he won't mind that she takes a seat next to him on the bale of hay. At least the cat seems pleased, now having two warm laps to plunder. "I'm so sorry, Michael. You're so nice and generous and wonderful..." Shouldn't she be saying these things to Simon? "She has to be just as good a person, and..."

She sounds like a better person than I could be, to overlook those kinds of things.