Maybe because he couldn't protect Lucas in his previous life, in this life despite not having memories, he was attached to Lucas since birth.
After he had gained consciousness in the world and met Lucas, he was charmed by him.
He would feel suffocated whenever he couldn't see Lucas. He had to have Lucas in front of his eyes, he wanted Luas to see only him like he only wanted to see Lucas.
Since they were children, Adrian had been obsessed with Lucas. He wanted Lucas only to play with him. He wanted all the things Lucas had, at first he thought he wanted to compete with Lucas and excel him in everything.
But he soon realised he couldn't be more wrong than anything.
He slowly realised his love for Lucas was twisted and had long turned to obsession and possessiveness. Even when he was only 4 years old, he didn't want Lucas to be with anyone else.
