He will be the one who almost always gives the reply to Nora. This is one of the primary roles.

He is Nora's best friend, respects her, and wants to protect her. But sometimes (almost all the time in the quotes), he thinks she is an idiot. He sees her companions as, at best, a merry band of kids that shouldn't have such an important role in the Commonwealth.

Then, he sees himself as a kind of guardian of order, if not of a kindergarten... 

More information about the Synth Detective and a snippet of his voice :
https://fallout.wiki/wiki/Nick_Valentine