I have to agree with fezziwig that I notice that I’m confused about this idea that D writing in Lily’s book somehow destroyed any hope of friendship between them. I don’t understand your scenario: you think Lily was upset about the writing, blamed Snape, but never mentioned it, and that was enough to destroy a friendship? And Dumbledore somehow knew that writing in a book would cause this effect? “I want to destroy Snape’s friendship… I know, I’ll write in his friend’s book!”
Given all the weird things that happen at Hogwarts, souls trapped in books and strange notes found under pillows and time travel, I kinda doubt Lily would stick to the hypothesis that it must be Snape, and never mention it.
I have to agree with fezziwig that I notice that I’m confused about this idea that D writing in Lily’s book somehow destroyed any hope of friendship between them. I don’t understand your scenario: you think Lily was upset about the writing, blamed Snape, but never mentioned it, and that was enough to destroy a friendship? And Dumbledore somehow knew that writing in a book would cause this effect? “I want to destroy Snape’s friendship… I know, I’ll write in his friend’s book!”
Given all the weird things that happen at Hogwarts, souls trapped in books and strange notes found under pillows and time travel, I kinda doubt Lily would stick to the hypothesis that it must be Snape, and never mention it.