Noa your dumbass, you should've warned Makoto right from the beginning you know? But no, you keep silent all this time and only warn him once he gets close to her.
Also Makoto had no choice, he was already treading dangerous waters after showing his disdain for the Water Princess.
People got beheaded for less than that, even if he helps the Light Hero. The only thing that probably saved his head was being the Hero's benefactor and friend.