O!Ciel also doesnt treat his other servants with the same harshness he shows Sebastian. To me that suggests his behavior isn't driven by hatred, but by fear. It's a defense mechanism, a way of asserting control over a situation in which hes actually the one with less power. (4\4)
To add to this, I think it's so sweet that despite his fear, and despite believing that both Sebastians disliked him, he still worried about them whenever they got hurt. 🥹❤️🩹 O!Ciel really has such a gentle & caring heart, but it was placed in an incredibly cruel reality.