It would have bee phony and cheap if the kid simply sat back, thought a moment and then accepted the news. Adults don't do that well. High school kids? Not so much.

The episode spent a good deal of time rather effectively showing just how alienated and alone that boy feels a lot of the time. When she tells him that she's been lying, he's faced with his own already rather large insecurities. I know from my own life experiences that when you suddenly have all your insecurities flare up in an exchange with another person, it doesn't tend to go as well as one would like. So, it wasn't a fair reaction. It wasn't a reasoned reaction. I WAS an honest and real reaction.