Kuro lost his parents at a young age, or rather,he killed them himself. Maybe because they didn't pay any attention to him,and even tortured him when he was young and that was the main cause lead him to have mental problems.Then he met you, a normal student in same school and also were his secret lover.

You find him in the dark of the dead end, his hands are covering with blood but that isn't his blood, that's the blood from a man he has just killed as that man dared to confess with you.