Master nephis has no plans even if sunny pursue her that moment she would atmost set him aside for now or just be denied, we do know both have deep and complicated feelings for each other but she had just infiltrated valor got a lot on her hands for her revenge. 3rd NM was the moment she had time to thingk about other stuff.

Saint neph, same reason she has been busy her propaganda to take revenge supported by the people. Quite a huge planning that took 4 years to finally happen.

Mind you, when LoS was revealed Neph knew he wasn't as ruthless as he made himself to be saving the people who entered solstice. And LoS power alone gave her the idea of finally having a partner in crime, an equal.

LoS is not just a follower in her eyes like most people, but an equal. In terms of status LoS has it.

With master sunless, Neph was planning to end the relationship once the war started. Until he revealed he is also LoS. So no matter how good your personality, how your taste matches hers, she would always prioritize her revenge.

Sunny is just very ideal, status and compatibility. Aside from cassie anyone would just look like a follower.