WOW, right now you are just an observer in his life. He doesn’t want your applause and he doesn’t want your approval. He just wants you to love him no matter what. Kol Nidrei night it is possible that the yetzer horah got to him or that he even went with his chevra to a minyan for boys like them and maybe he didn’t like it. For Neilah, the Yetzer tov got to him and he felt a need or a stirring or whatever and it was his choice to do what he did. In addition it was very possible that he and his friends discussed keeping Yom Kippur both before and after. Just take a step back and see what develops without judgment one way or the other. Give him some slack and let him guide you.
Hatzlocha.