This is a wonderful story. Breathtaking, emotional, poignant without being sentimental. Great characterisation, lovely attention to detail, smooth transitions between the two POVs. The dialogue is natural, although the metaphor explanation is a bit long. The relationship between Molly and Neville is unusual but so well-developed.

I love the ending paragraph, and I love the usage of future tense for the last couple of sentences e.g. "Neville will write to Romilda...Molly will smile and give advice."

That was perfect. Thanks for writing this.

Your Neville. Just... your Neville. His confusion after sleeping with Romilda. His attachment to his parents. You've got him down and I love him.
Molly's quiet desperation is lovely, as well. I normally don't read AUs, because they're rarely done as well as you've done this. Watching Molly try to piece together her family after Arthur's death was heartbreaking, but there was a certain grim determination to it that kept her from seeming completely helpless - which is definitely in line with her character.
The discussion about half-lifes was a little odd, but made sense once I thought about it for a while. Not a concept I ever thought I'd see come up in a Potter fic. :)
And like Soraya, I'm relieved that you didn't ship them!