Before Iris went to the capital city, she followed Cane to the black market as well while Jace would always be left behind to take care of the pack every time the Alpha went away. As such, the time he spent with Iris had always been very limited. They were at most at the point of being courteous with each other, but he had not yet reached the point of trusting her completely.
Unlike Ethan, Jace was still thinking of Iris as a member of the Blue Moon pack and not one of them.
He also always thought Cane treated Iris considerately because he needed her, since he had to get a grip of the Blue Moon pack and the whole magic stone mine. Moreover, she held some of Cane's secrets and the fact her presence eased Cane's transformation during the new moon justified his need to take her whenever he went away.
However, what Jace witnessed just now was simply too shocking to be believable.
He kissed her! He kissed the tip of her nose!?
