You can totally see it coming. When Harry tells Hermione that Severus has been making poisons and caching them about the house, I knew it would end in tragedy.
Severus was probably making them because he really wanted to be talked out of taking them, but putting them in accessible places so he could get them in an instant and not be denied the comfort and finality of Death, should he so choose.
Really, it was out of the mouth of babes when Teddy tells him that Harry is Belle and Severus is the Beast. The rude neighbor only finished it for Severus. No one without a vested interest would ever see Severus as anything other than a DE, no matter what the truth was, and he knew it.
This work is a literary masterpeice! Beautiful, poignant, and heart-wrenching. Thank you!