Author note: I intended the story to stop here, and it is probably better to do so. But people in the comments asked for a bit more, and… well here is a vignette from Hermione's point of view, about a thousand years ago. Dedicated to the partners of people with depression.
Jealousy would be much easier to handle. It would even be understandable. After all, Hermione got to do things, and not only that, but do them publicly in the guise of the coolest person in all of magical history. But no, Harry was too noble – or rational – to be feel any resentment towards her. Instead he got depressed. Whatever his other manifold virtues, living with a depressed person for centuries was horrible.
The first couple of years were pretty good. They were busy getting themselves established, and they had been very satisfied with each other as friendship turned into romantic love. Harry's manic energy and clumsy attempts to do everything optimally were at the least endearing. They had rapidly acquired massive power over the years, with Harry's ingenuity and her blazing, diadem assisted intellect. He wasn't even jealous of that, the ultimate in enlightenment.
But then the grinding misery of their position became, well, life. They were there to endure. To see horrible things happen to people, and to mostly not interfere. For they knew for sure that disrupting history would cause the universe as they knew it to cease to exist. There was even the possibility that it could wipe out all universes, given the timescale of their jump. Somehow that must have taken an absurd amount of energy.
Instead they had to watch, assiduously checking with Hermione's perfect memory of the history she happened to have read. They assumed that as long as they did a reasonable job of the big things, the small ones would sort themselves out, as, after all, they already had. Harry was truly learning to lose. To give up things he cared about deeply, for the long term goal of becoming wise enough to pass his own – presumably – test of "experience". And if he failed – if all the suffering was in vain – then the world would lose its benevolent god. And possibly cease to exist too, for that matter. For how then would the key Harry had made have conceivably come from?
So, watch misery helplessly, stressed out about becoming worthy of being a god. Depression replaced manic energy as striving got replaced by enduring. Hermione took it badly. Harry took it exceedingly badly. Possibly the worst part for her was to see the husk of Harry spending most days unable to get out of bed.
It had been even worse now, as the time of Hogwart's founding approached. Soon Hermione would get to be Rowena Ravenclaw, and do things. It is not as if they had never taken on the appearance of some other history maker who as it turned out didn't actually exist, but Rowena would definitely be the most fun. Fun that Harry could not participate in.
Harry had felt a little better when they found the parents Slytherin and cast mighty protective magics on baby Salazar. Harry had dreaded having to play his role, the obvious choice. Although the way things were going, Hermione had seriously considered assassinating the now seven year old kid. Surely Harry would be better off doing something. It would be unfair on Salazar. But a sane Harry was pretty important for the greatest good for the greatest number.
So it was a surprise when she walked in the door and saw a beaming Harry dangling from the ceiling, toes hooked over a joist. "I've been checking up some remote possibilities. Guess who doesn't exist?" he asked. Before she could answer, he clicked his fingers for the first time in two centuries, and a huge silver sword appeared in his hand, nihil supernum engraved on it.
Harry grinned.