Harry was alone.
It was that simple.
There was no heart-wrenching betrayal, no noble and heroic death on the battlefield, no mass slaughter of all those whom he cared for.
He was just alone.
Luna and Neville. Hermione and Ron. George and Angelina. Ginny and Dean. Cho and Viktor. Draco and Blaise (that one was a shocker). Remus and Tonks. Sirius and Emmeline. Severus and Narcissa. Dudley and Marie (a very sweet young woman whom he had met in college).
Even freaking Dobby and Winky.
Wow. House elves had more of a love life than him. That was just sad.
Harry was alone, left behind in the dust and rubble of the war. Not on purpose, of course. Everyone just sort of drifted away, and he didn't notice until they were gone.
And how was he supposed move on? Find love? He didn't even know how to love someone properly due to his severely lacking childhood, so it was no wonder that his few attempts at a romantic relationship ended in disaster.
So Harry was alone.
And loneliness really is one of the absolute worst feelings.
So one day, about two years after Lord Voldemort's defeat, he just got up out of his bed in his lonely little house that no longer received visitors, packed all of belongings into a trunk which could be used as an apartment if need be due to its expanded interior, and he left.
Harry James Potter-Black travelled the world and learned all the spells and rituals anyone could ever hope to know, even venturing to the non-magical world and keeping up with the latest advancements and discoveries, and before long, ten years had passed, and ten more, and ten more, and ten more, and ten more, and then Harry realized that over a century had passed and that he was growing old and tired.
And Harry was alone.
The last of his friends and family had passed away about a decade before, and there was nothing else left for him to learn, to explore.
So Harry James Potter-Black made one last trip and returned to Godric's Hollow, the place where it had all began, and slowly climbed the stairs leading up to a small nursery with half of the wall missing, and he sat down upon the floor.
He surrendered to that awful, aching emotion bubbling up in his chest and choked on a sob as it overcame him, drawing him away from this life and into the supposed Next Great Adventure.
Harry was alone.
He died alone.
And loneliness truly is one of the most terrible of feelings.