Fortunately Bella is pretty smart. After a moment of silence, she finally understood what Arthur meant.
Her gaze on Amanda became a little strange.
"You gave him your body without any special relationship?" she asked.
This is actually an inappropriate question to ask even though they are siblings.
Amanda cleared her throat, looking at her with bulging eyes as she replied, "that's none of your business!"
Inwardly she said, 'what's wrong, I like that, and I'm sure in the future our relationship will reach that point.'
Amanda's confirmation made Bella turn her gaze to Arthur.
Another reason the question was inappropriate was because she herself had once tried to tempt Arthur into doing that with her. Only, Arthur did not respond.
Now; she wonders why Arthur agrees with Amanda but disapproves of her. Does he find her less attractive?
Thinking about it pissed her off a bit.