I mean, I get it. He's barely 18 and his mom just disappeared. They let you buy cigarettes at that age, but that doesn't make you a mature and independent adult who will never ever need their parents ever again. And he probably feels like someone he genuinely loved disappeared from his life because he personally failed her. And it's a mother figure! He already lost one mom and now his replacement mom just up and left and he had no idea that she would ever plan to do that.