Mabel's wedding was down in Los Angeles.
She hadn't been able to hold it in Gravity Falls—she'd told Dipper something about her fiancé Henry's grandmother having a bad knee and not being able to travel that far—so instead she sent Dipper a package full of photos, favors, and even preserved flowers from the decorations.
The day it arrived, Dipper spent the afternoon at the kitchen table in the Shack, poring over the pages of a wedding scrapbook Mabel had put in, with pages of photos of every detail. He could remember when he used to be annoyed at the level of detail she included in her scrapbooks, but now he could appreciate it. Seeing all the little details like this, he could picture it better, almost imagine that he'd been there with her.
But of course he hadn't.
He'd been stuck in Gravity Falls for years.
He didn't mind it all the time. Exploring the forest and expanding on the Journals took up a lot of his time and didn't leave much room in his head for thoughts about anything else. It was only when he went to bed that the thoughts of what he was missing, of what he could have had, started to swirl in his head.
Needless to say, he didn't sleep much these days.
(Instead, he'd go three or four days without sleeping, then pass out somewhere from sheer exhaustion. Stan would usually bring him a pillow and blanket or something, and he'd wake up a dozen or so hours later, completely disoriented.)
Dipper ran his fingers down a page where Mabel had stapled a scrap of fabric torn from her veil. He could feel the soft, sheer fabric, cool against his fingertips, and his eyes were fixed on a picture of Henry flipping the veil over Mabel's forehead where you could see it floating, apparently weightless.
Dipper smiled and wished he could have been there to see it. Of course, even if he could have left the town, it might have been awkward for Mabel—he hadn't been the best with people even before that fateful summer when they were both children.
He flipped the page again, to a two-page spread of pictures of people moving into the reception hall. Dipper recognized Cousin Terry, who looked significantly taller than he'd remembered, and his parents, and of course Candy and Grenda in their bridesmaid gowns. Everyone was smiling, caught up in the happiness of the wedding, and Dipper found himself smiling too.
When Stan walked back into the kitchen later that night, he found Dipper sprawled across the table, asleep with his head on his sister's wedding scrapbook. He shook his head and pulled the book away before Dipper could start drooling on it, smiling as he rifled through some of the pages. He'd intended to stay home from the wedding with Dipper, but his nephew had pushed him to go, to not miss Mabel's wedding for his sake. He smiled at a picture of Mabel dancing on top of a table, remembering how she'd broken into impromptu karaoke and dedicated her song to her brother.
Stan turned, still smiling, to look at Dipper, who was still passed out cold on the kitchen table. Stan sighed, still smiling fondly, and trudged to the living room. He grabbed a blanket and a pillow from the armchair and brought them back to the kitchen, carefully resting Dipper's head on the pillow and draping the blanket over his narrow shoulders.
When Dipper was asleep like this, the adult expression fell off his face, and Stan found it hard to remember how many years had passed since the summer the kids had come to stay with him. With Dipper asleep, looking as young as he did, he could almost pretend it was still the summer of 2012, that Mabel was just in the next room over, about to come in with a grin that showed more braces than teeth and possibly some more teasing about how she was a millimeter taller than Dipper.
You couldn't tell that the two were twins anymore. Every time Mabel came back to visit in the first few years, she seemed to have shot up another foot, while Dipper . . . hadn't.
Stan flipped to another page, where Mabel was throwing her bouquet to a crowd of girls. She was practically glowing with happiness. It made Stan wonder what Dipper might have looked like, at his sister's wedding or his own, if he'd never come to see Stan. It was a stupid thought, of course, because Dipper was stuck here, and wasn't able to go to his sister's wedding, and would never have one of his own.
Stan glanced back at Dipper, still asleep at the table, his body still small enough that he could have used the table as a bed.
It was some kind of cruel joke, Stan thought, that in the same way that the twin who had most wanted to explore things had been trapped in a single tiny town, the one who had most wanted to grow up never would.