Looking up at her partner just before she starts to pleasure her friend.
With Devotional Sex any activities with others are first sorted out at the relationship level - he can set what she can and cannot do with others, and she can set what he can and cannot do with others. Once agreed Devotional Sex takes over and as long as everything stays within their agreed limits, she decides what will and will not happen.
Perhaps when he agreed that she could enjoy other men he never thought that she would do this. The look she is giving her Knight here suggests that she is saying to him “Look, I’m really doing this, and it’s fun!”.
Devotional Sex treats such adventures as closer to swinging than cockholdry.
Most cockholdry on the internet is mainly about her partner feeling humiliated and inadequate, and her being a slut for her ‘bull’.
With Devotional Sex the above adventure does have the Knight under his Princess’s power. There is room to enjoy slight feelings of jealously, enhanced by knowing that the friend may soon ejaculate but he will not be allowed that pleasure tonight. But her Knight doesn’t feel humiliated or inadequate - he is still her valued and appreciated partner.
And she is not a slut, but a Princess who is in control of what happens.
So as she looks up at her Knight, though seeing that he is slightly jealous, she also sees that he is also getting a thrill out of this adventure.