Another thing to note was that Nolan knew Stella and her feelings for Kyran way longer before Cyneah came into the picture. He even considered supporting the former because of how much she was willing to sacrifice to help Kyran.
However, Nolan ultimately decided to support his nephew's decision. Besides, he appreciated how Cyneah gave Kyran a place to rest.
Kyran likely did not realize it back then, but he was too unstable to be left alone, and Nolan feared he would self-destruct. Fortunately, Cyneah gave Kyran a place to unwind. She did not even have to do anything because her presence alone calmed him and lowered his guard.