I might be in the minority, but I enjoyed this one and I'd be melancholic when it will end. Don't get me wrong, if I was in charge this thing would've lasted at most up to chapter 100, but overall it was one of the best for me.
Wasn't Nagini his first disciple? If so, yeah, he would be mad that his only disciple (for time being) is being treated badly. Add on to the danger to town he frequents to and forest (for now) which is his home. Yeah, that dragon's done for.