Nick is a very complicated person who's been through a lot of trauma. I don't really delve into what happened when his mum had her initial breakdown in the story, but at the time, Zoë was at uni and Nick was lone in the house with her, and only ten years old. Add to that a lack of friends, occasional bullying, witnessing his mother's suicide attempt and finally, only weeks later, what happened with Craig, and he was bound to break at some point. I think a lot of my adult readers forget that Nick is only 17 years old at this point in the story. And he's had to carry a lot more than any 17-year-old should. So I'm glad you feel sympathy for him. He's not a bad person.