That's what you get when you have little faith to yourself that certain confidence in yourself that makes you think that he is yours and you're worthy. But i guess since kotaro is still a student and has not proven himself yet to the society he must've been a little bit insecure and must've felt a little bit inferior for being young. He just needed an assurance from the older guy and stop assuming things. I hope the older guy in the relationship cn guide the younger one too, he's the source of kotaro's insecurities anyway but he's a such weirdo
Even if he didn't do anything, I still think he's an ass for leaving kotaro when he came over and basically neglecting him when he came back. Kotaro deserves better than that.
Nuuuuu! THE ANGST AND HEARTACHE KILLS! AUUUUGH
ヽ(`Д´)ﾉ
Calm down, he didn't do it!