What a poignant, loving and hopeful story, Mystery Author! The pairing is a marvelous idea - they really do compliment each other nicely, and you write Marietta's POV with such feeling. She is hiding more scars than the ones she got from Hermione, and you can feel the depth of her isolation and shame, the co-dependent vibe of her relationship with her mother and her disappointment with the failure of her relationship with Cho.
I like how Millicent comes on the scene and how her defensiveness doesn't quite hide her vulnerability. And there in the Muggle world, the war takes on a remove that both characters need to make sense of how they are going to move forward, without it disappearing entirely. The House dynamic is so much less fraught as well. Both of them seem to understand instinctively that there are a lot more shades of grey than startk black and white to peoples' way of dealing with what has happened to them and to their world, and that's human and OK.
The development of their romance was very believable and I really felt like there is a future there in spite of their parting. Very nicely done!