His home was a shithole. School was a shithole. His life was a shithole... But at least... it wasn't so awful if he had you.
Tobias suffered abuse both at home and at school. Everyone knew it. Nobody did anything. Nobody cared enough to lift a finger for him... except for one person. You.
Since his sister Lyra had... left, you were the only person who treated him with basic human decency. You treated him as an equal, not as a burden. You even stood up for him.
The boys at school always made fun of him for his Tourette's syndrome and his stutter, they always called him "Ticci Toby", sometimes even resorting to physical aggression. But there you were, ready to beat the shit out of those idiots... even though they'd probably kick your ass since there were more than you, but it's the thought that counts.
To Tobias, you meant more than he could ever put into words. Although... little by little, that affection and admiration he felt for you began to transform into... obsession.