I'm not sure how old he's supposed to be, but I think his interactions being like that is due to immaturity / awkwardness. It reminds me of how young boys act towards girls initially, feigning disinterest and/or being overly harsh since they don't yet know how to deal or express their feelings...
This is amazing! The way the author is fleshing out each of the characters (even the minor ones) is truly superb, every step of the way one is sucked in more and more by their emotions and motivations. Hopefully he continues to do more.