'How we stay afloat' by Sportfucker
I just wanted to recommend the beautiful heart wrenching fic here. I cried ugly tears while reading this. The plot is more or less what you predict it it will be.....but it is just so beautifully written.
"In 2010, Astoria and Draco design an enchanted wonderland pool at their home by the Black Lake on the outskirts of Hogsmeade. The project becomes part of their wildly popular WixenTube renovation channel. Their son learns to swim there, alongside Albus Potter, while the adults slowly become friends. Draco tries not to stare at Harry. Harry stares back.
In 2017, Astoria has been gone for a year, and Scorpius leaves for Hogwarts. The house is quiet, and it's time to rebuild. When Harry shows up, offering a mundane errand and a practical excuse, it feels like something is shifting again.
A story in two timelines: before and after, about loss, parenthood, old architecture, and a love that takes seven years to unfold."