Why did Sayoko Nanomori stab Itsuki?
At this point in the story Sayoko had lost her mind. From the moment Itsuki found out that Sayoko had been cooperating with Makoto about the secrets of Quon, Sayoko has been since then roaming around discontent. We see scenes of her in the beach completely filled with grief, and a certain scene where she flipped on Ayato. From that moment on her sadness, disappointment, and perhaps even anger has been accumulating. It all exploded when she saw Itsuki one last time while he was holding a gun to Bahbem/Helena. I can only conclude that she figured if she can’t have Itsuki for herself, then nobody else will. So Sayoko, at this point it is apparent she’s out of her mind, stabbed Itsuki. Once Sayoko realized what she came to a startling realization of what she had done. After this we get to hear Itsuki’s last few words, and I have to say they were suprising since they were words of kindness and regret. We get hints that if Itsuki were to repeat it all again, perhaps he would have given Sayok
