Harry thinks it's funny that muggles call depression the black dog, given his personal history. He tries to remember that when it circles back around to him-he had thought himself haunted, hunted, once, but in the end, it was only family he didn't know he had.
He is content most days. Some days transcendentally happy, of course.
And yet.
He will see it at the far reaches of his vision, and wonder when it will be back. He sends off an owl for help when he thinks it's drawing near, and sometimes that's enough to drive it off. Sometimes he rounds a corner and it comes barrelling out of the darkness and it catches him by the throat, and then he thinks this is it. Sometimes it only holds him with a retriever's soft mouth and then lets him go, as if to remind him of how fragile life is, how quickly he could lose it, how much he still has to be grateful for.
He still carries the old marble with a snake at its heart. He remembers that the Dark Marks, which had been created in part by the Protean Charm, like the marble, had faded upon Voldemort's death.
So he finds it comforting to roll it around in his palm, to carry it like a worry stone. He had the thought, once, that maybe Snape gave him the original, and it would stay in his pocket no matter what. But it's still layered in spellwork, and he can't imagine all that lasting much beyond its creator's death.
He's still immensely relieved every time the magnificent eagle owl visits. Even if it's impatient and nippy, like its master, and shows up with no set schedule. Sometimes it brings a short letter: "Beaches are teeming. Still nicer than England." "Saw your wife's first byline. Tell her her writing has improved." "Neither of you should be allowed to name anyone or anything. Congratulations."
Sometimes it's just a package: sweets for the kids. Books, often, that Harry gamely tries to read and sometimes even finishes before passing them off to Hermione. (He thinks they're usually really meant for her. It's one of his goals to get them to mend fences for good.)
When they'd bought the house, a package of black-hearted anemone bulbs showed up that bloomed in a riot of colors in the early spring. When Al was just turning six, it was a vintage Gobstones set, Bernie Bott's themed-sometimes the loser gets blasted with something foul, but sometimes it's something pleasant, like apricot or honey. The uncertainty is half the fun.
He still wishes Snape would give more notice when he's back in England and plans to stop by.