He is careful and clumsy and not terribly clever and she is carefree and elegant and lively and somehow they work.
He meets her in the most clichéd place possible: in school, which isn't very surprising, seeing as it was also the place where he spends the majority of his time. He remembers glancing at her while she was having dinner, telling tales with a huge smile and lots of hand gestures, and thinking that she was pretty.
It doesn't take long before they properly met. A moment in the hallway, accidental stumbles, and he almost literally falls at her feet. She just laughs and helps him up. He doesn't get more than a name and a smile before she disappears again and for a moment he can't help but wonder if she wasn't just a figment of his imagination.
They meet several times after that. She's everywhere. In the hallway when he's walking to his next class, at the lake when he's trying to read a book (needless to say that didn't really work, certainly when she was this close), even in the infirmary after he's had an accident in Potions she's there, and he wonders if she's always been here, because he can't remember a time that she wasn't.
One day, he gathers all the courage that his House is so famous for and asks her out. She seems surprised, but the delight in her voice is real when she agrees. Their first date is followed by many more and eventually he kisses her. It's soft and passionate and wonderful and he doesn't think he can be any more happy.
After Hogwarts, he becomes and Auror and she becomes a Healer. Every night when she comes home she finds comfort in his arms, safe from the horrors she's seen and he finds relief because no one hurt her like the villains he captured so commonly menaced.
They keep up this pace for a while. He arrests villains, she heals people the best she can and every night they fall asleep in each other's arms. Nothing changes their routine, not even when they get golden rings on their fingers, and none of them minds.
Once he wakes up in the middle of the night to coughing and a soft whisper. "Hugo." She sounds frightened and weak and his instincts are supposed to kick in but he freezes when he sees that the sheets are dark stained with blood. "Saint Mungo's", she says barely audible and he gives himself a mental kick in the butt for freezing.
She lays in a bed, looking fragile and almost as pale as the stark white sheets and oh god, he nearly forgets to breathe. She awakes with a jolt and he tells her to lie down again. He wants so badly to hold her, but instead he just holds her hand and tells her to keep breathing. He almost expects a cheeky grin and a "Well then, because you asked so nicely", but instead he gets a weak smile that makes him want to sob. He holds it in, because one of them has to be strong.
He sings her a lullaby and watches as she slowly loses consciousness and thinks with all his might "Keep breathing, just keep breathing".
And breathing she does.