The Sapiosexual Submissive and Her Cuckquean Fantasy

Cuckqueaning is a form of voyeurism where a woman derives sexual pleasure from seeing her partner with another woman. In the world of D/s, a dominant will often include the submissive cuckquean in the scene.
In a D/s session, each partner objectifies the other and each stays in their role, as either dominant or submissive. When the session is over, each participant is simply a pile of flesh and generally uninteresting, unless the partners also have a real world relationship as Duncan and Lydia do. But it is crucial that these two worlds are kept compartmentalized.

Lydia has a voyeuristic streak and wants to include her friend, Rachel, in one of her's and Duncan's D/s sessions. This leads to both Lydia and Rachel wanting more.
Since Duncan has wanted a threesome with Lydia and another woman, all three are most agreeable.
Their sessions are full of pure sexual pleasure. But when Lydia's emotions enter into the mix, they create insecurity in her. While Jealousy happens easily in the real world, it should never enter the fantasy world because it denies the authenticity of being that particular object there. But Lydia blurred the lines between the two worlds that she and Duncan share. She tells him they cannot continue.
Now, months later, she calls him hoping to reconnect. While he still cares for Lydia, Duncan explains there can be no going back. Can they find a resolution to move forward, or is this it?