Evan knew how Niks felt with the new sights and smells and senses in general. He wanted to tell her that he understood exactly how she felt, but couldn't get a word in between the two.
When she left, he watched her walk away, not knowing what to do. What would anger her more? Him standing there like an idiot, or him chasing after her to try to help her feel better? So he stayed.
He expected something from Simon after she was gone, some snide remark, but the fairy didn't say or do anything. Or even acknowledge that he was standing there. Apparently, for Simon, civil was ignoring that somebody existed. Evan felt like he could handle that. He was glad when Simon melted back into his own room.
It left Evan with nobody, however. He decided he should try to find out more about where they were, and if there was tea.