Eren's always been a psycho. What 8 year old looks into another 8 years olds eyes and starts worsipping him as blonde savior and decides to dedicate his whole life to the freedom-scenery from that kid's book? What kind of kid kills 3 people for "muh freedom" and preaches about how everyone who likes quiet family life are sheep and cattle and wants to destroy the world because his headcanon about the book didn't come true and sacrifices every single family member for his dream of freedom and traumatic "everyone like Arumih" ending?
Eren's insane. School Eren has the same personality and daydreams about creating threat to all humanity because his life is boring. Eren is better off dead