Hermione should have known that a relationship begun in battle wouldn't survive peace.
Their first row as a couple is over whether it is too soon for Ron to leave the Burrow. A week later they move into a flat together, where she silently resents Ron's continued reluctance to do any cooking, and he glares whenever she brings it up. Barely two month later, he moves out.
"I'm leaving it behind this time," Ron says, tossing the Deluminator onto the floor at her feet. "So don't get your hopes up."
Unexpectedly, Hermione doesn't cry. Somehow that makes her feel worse.
Ron moves into Harry's spare room, and Hermione gets a cat. She knows better than to ask about how Ron's doing.
Perhaps she shouldn't have looked too closely either, because when she notices Ron's eyes lingering on Harry's face, and sees Harry's fingers close around Ron's wrist, the room swims before her eyes.
She goes home to a flat that feels colder and emptier than ever, and ignores the next three Owls from Harry. After that, the Owls stop coming.
Harry Apparates into her living room a few months later.
"We broke up," he says, and then "I miss you."
She and Harry date for four months before he buys a house with the inheritance from Sirius. Hermione pays for the bills, they start planting a garden, and have comfortable sex once a fortnight. It feels strangely as though they're pretending to be adults.
Neither of them have seen Ron since the second time Harry slept over at her flat, when Ron quit his job and disappeared. According to Ginny, he's gone traveling to 'find himself'.
"How is he?" she asks, over brunch.
Ginny makes a face. "Angry. Confused. I think if he knew how he felt, he'd tell you."
Ron arrives on their doorstep early on a Saturday morning.
"I've figured it out," he says, when Hermione answers the door in her dressing gown.
"Harry!" she calls. "I think you'll want to see this."
"There needs to be three of us," Ron explains, while she sips coffee and Harry makes toast. "It doesn't work otherwise. It's..."
"Unbalanced," Harry says.
They both look at Hermione.
"Do I have to decide for us all?" she asks, cradling the mug in her hands.
"I've decided what I want," Ron says, stealing some of Harry's toast. "You can just say no, or yes."
Important decisions are never as simple as yes or no. Hermione needs more data, and space to think, but finding space is a challenge now that Ron's sleeping down the corridor.
"Stay here," Harry insisted, his expression daring her to disagree. "We've got loads of room."
At some point during his travels, or time living with Harry, Ron has changed. He cooks them a spicy chocolate stew for dinner, and the next day she finds him efficiently washing clothes with a spell that sounds like Arabic.
"How's the data collection?" asks Harry, as she slides into bed.
"...promising," Hermione says.
At first, she can almost pretend that Ron is just a guest. He joins them for meals and helps around the house, but Hermione curls up with Harry every night as if nothing had changed. Ninety per cent of the time, her interactions with Ron are purely platonic.
The other ten percent are unsettling. One morning they almost collide in the bathroom doorway, and Ron's eyes slide over her body, which feels all too naked beneath the towel.
"Um," Ron says, stepping closer, and brushes a lock of wet hair away from her face.
"Excuse me!" Hermione squeaks, darting away.
When she walks in on Harry and Ron kissing in the kitchen, it's a shock.
For a moment Hermione can't seem to breathe. She just stares, taking in how Harry is pressed against the cupboard where they keep the mugs, his hand fisted in Ron's shirt.
It feels like something she shouldn't be watching, but Harry is her partner, and Ron is...Ron is...
She backs away, knocking into a chair that falls over with a clatter.
Ron jumps away like a shot.
"Is this a problem? Should I have waited?"
"No," Harry says, still holding onto Ron's shirt tightly.
"I can leave," says Hermione.
She's contorted on a kitchen chair, arms wrapped around her knees, with Harry sitting opposite. Ron is standing by the wall with his arms crossed, looking uncomfortable.
"If you'd rather be together, I'll move out and--"
"That's not what I want," Harry interrupts.
"You want him," she says, staring at her knees. "We hardly ever have sex."
"I want you both, Hermione," Harry says. "The three of us, together."
There's a tense silence.
"I'm scared of ruining everything," she whispers.
"Me too," says Ron.
"We killed Voldemort," Harry replies, looking stubborn. "We can do this."
It's the most nerve-wracking thing she's ever done, which is ridiculous because she's kissed them both before. There's no reason for a threesome to be more than the sum of its parts - except that if it's not, it won't work.
"Hermione," Harry says quietly, and she closes her eyes and leans in.
The kiss is dry, gentle, and she doesn't open her eyes when Harry pulls away. A moment later another pair of lips brush her own, warmer, and a hand touches her hair.
She sighs, deepens the kiss, and lets herself fall.
"Harder," pleads Ron, as Harry's hand slides down his cock. "I won't break."
"He's too single-minded," Hermione says, rocking over Harry again.
She circles her hips, muscles squeezing Harry's cock and her breasts swaying in front of Ron's face.
The sex is confusing and too awkward to be entirely satisfying, but she can see the potential.
"This is hard!" Harry protests, looking from one of them to the other.
"You just can't multi-task," Hermione retorts, grabbing Ron's hand, and guides it between her legs.
It's a start. Within two weeks, it's brilliant.