i should explain.
sybil, or todd as you know him now, had almost always been followed by the tall man, mostly because his father had been followed since he was young. it was no easy task for either of them, so sybil decided as soon as he was old enough, he would leave and start a new life where the tall man could never get him.
but sybil didn't know that it doesn't work like that.
there was another boy sybil knew who went by the name of todd. the two of them were very close. todd was also followed by the tall man, but for some reason, was no where near as upset about it. sybil would talk about how the tall man hurt him, how he couldn't breathe or see when the tall man was there, but todd would always talk about how everything seemed calmer, and more in place when the tall man was there. todd and sybil didn't talk much after that.
then one day, a few years later, todd came back and asked sybil over to his house. sybil came, and todd closed the door behind him and tried to kill him. but sybil managed to overpower todd, despite todd being, at the time, much larger than sybil. it was that day that sybil decided to leave.
sybil changed everything about himself, starting with his name. he decided to take todd's, because he had always liked the sound of it. sybil was now todd. sybil was always considered selfish by his friends, so todd decided to become the most selfless person he could have been. his mom had always said sybil was a big whiner, so todd decided to try and keep his mouth shut as often as possible.
but todd didn't understand that creating a completely new personality doesn't work like that.
remnants of sybil still remain with todd to this day. while todd was on the run, sybil had always been watching through the same eyes as todd. but when spencer came along, sybil was forced into a dormant part of todd's brain, and he's has been waiting ever since. and he's been hurting.