Because Usui's perpective is mostly a mystery, there's a certain type of fun in wondering what goes into his mind and the reasoning for his shift in attitude. I personally think Usui, while becoming more solemn in attitude has also become more sincere with Misaki by being less teasing. In return, Misaki is forced to confront her own feelings that she's been in denial as she is gradually forced to be honest with herself and Usui.