I have no idea what you are talking about. Kanna spent an unknown number of days hiding away, pretending to be sick because she was unable to do more than cry - and you talk about everybody simply smiling? Tetsuro is Tetsuro, and didn't end up doing anything else but kicking the fence and hurting his foot, but I hardly saw him smile away the emotional pain after his doomed-to-fail confession. It's true the bigger picture was pretty clear to all of them from the beginning, and that could have, to a degree, forced them to look like they had a mature stance, but that's it. Kanna's last useless confession came after Tetsuro's useless confession - and it was purely for her own peace of mind, signifying the same thing she told Tetsuro: That she can't forget Kaito. That's the opposite of casually accepting they can't have their loved one. Also, neglecting Tetsuro's feelings for her and Kaito and Ichika's for each other have got nothing to do with that. She can't magically start to love Tetsuro, and Ichika herself thinks it was due to Kanna that she got together with Kaito.
I hope you weren't looking for some bitchy polygon drama you find in stock shoujo or tv live action, with all the backstabbing and whatnot, that should result in everybody hating everybody enough to kill them instead of pairings based on love. I preferred this show's approach much more.