It started because yours broke.
Clasp just gave up entirely, which was genuinely impressive timing given you were supposed to be leaving in twenty minutes. You stood in the middle of Lottie's bedroom holding it and staring at it like it had personally betrayed you.
"Lottie," you said.
"Yeah?" she called from the bathroom.
"Can I borrow one."
She appeared in the doorway immediately, toothbrush still in her mouth, looked at the broken clasp, looked at you, and pointed at her drawer with the toothbrush like she was directing traffic.
"Third row," she said, through toothpaste. "The good ones."
She came back in properly, face washed, bright-eyed, and watched you look through the drawer with the focused interest of someone supervising an important project.
"Not that one," she said, appearing at your shoulder.
"Why not."
"The wire's gone weird." She reached past you. "This one."
"Is it comfortable?"
"It's my favourite," she said. Like that settled it entirely.
"Lottie that's your favourite—"
"You can borrow my favourite," she said. Very earnest. Like this was a significant gesture she was happy to make.
You looked at her.
"It runs small," she added helpfully.
"How small."
She tilted her head and looked between you and the bra with bright considering eyes.
"Try it," she said.
It fit. Technically.
"Technically," you said.
"It fits!" Lottie said. Genuinely delighted. Like you'd both achieved something.
"Lottie—"
"It really fits," she said, tilting her head the other way now, looking thoroughly pleased with this outcome. "You look—" a pause, a smile she didn't bother to hide — "really good actually."
"You have to say that," you said. "You're my girlfriend."
"I don't have to say anything," she said brightly. "I'm saying it because it's true."
You wore it.
What you did not anticipate was Lottie being completely useless for the rest of the morning in a way that was very unlike her and extremely flattering.
"You keep looking at me," you said, over coffee.
"I'm not looking at you," she said, looking at you.
"Four times in the last minute."
"I'm thinking," she said.
"About what."
She smiled into her mug. "The bra."
"Lottie."
"It's mine," she said, completely sunny about it. "I'm allowed to think about it."
You pointed at her. She grinned.