Nestor Nik holds an absolute grudge against Aeyron Archer and the victors of The Youth Rebellion. Nestor chose the wrong side in The Youth Rebellion and he had to bend the knee to Aeyron for his survival, not only did Nestor have to face that humiliation he had his title of Warden of the South stipped off his, and given to Lord Ben Royce. How could Nestor take that? He rules The Hunter's Gift, Ben Royce answers to Nestor but Ben Royce is the Warden of the South? It's insulting to Nestor. We mustn't forget that Nestor has a personal grudge to Samuel Royce for sleeping with Nestor's bride-to-be Brielle Storm. When Samuel arrives back to Cephri months before the events of the book Nestor is insulted ONCE AGAIN. Aeyron exiled Samuel to appease Nestor but he's brought back him.
Nestor begins the seeds of rebellion, he already has contact with many people at court and at court is where he begins his faction. There are also many other lords who have felt neglected by Aeyron's rule and they join up with Nestor. Therefore Nestor is able to mobillise the feelings he feels against the crown, and when Ulthor's grievances with Aeyron are aired then Ulthor and Nestor join in some sort of super pact. Nestor and Ulthor have the support they need, all they need to do is just find a means to start the rebellion.
Nestor is not physical, nor is her dominating but when he has Jon Darklyn captured now he has the time to be those things. He tortures Jon and abuses him, feeling finally superior to someone like him. When he is in the prescence of anyone else such as The Mountain he cowers away from any conflict, when The Mountain wants to ride out and chase after Jon Darklyn Nestor refuses, but The Mountain keeps on testing him.
There is the saying that there is more than meets the eye, but in this case it isn't true for Nestor. His ideals are plain to see.