Brilliant!
Of the several stories that I've read so far, this is the one I've enjoyed most. I really enjoyed the non-traditional structure; it's the kind of format that's simple but difficult to truly pull off. I thought your approach was most effective here.
In Part I (It happens like this ...) I absolutely loved the awkward conversation between Harry, Draco and Astoria. That was one of my favourite parts of the text; there was something about it that really rang true. Also highly rated are the conversations between Ginny and Harry in Part II (—No. No, it doesn't happen that way. Like this:) and Part IV (Not quite. Go further back:). They seem like such realistic conversations for a married professional couple/new parents to have, and display really good characterizations of both Harry and Ginny. I'm starting to think dialogue might be your greatest strength, because your conversations are nuanced, but not out of the everyday.
I really, really appreciate that you wrote Ginny as an actual character and an actual person, because too often in H/D fics she is just a caricature or tossed aside.
I had certain minor quibbles but overall, I loved this story! Will definitely be rereading it and if I ever write that bloody recs list I've been threatening to compile, I would certainly add this. Thank you for writing!