Jim missing Cece's recital is what makes Pam realize she's falling back into her old ways. She's accepting things she doesn't want to accept and not standing up for herself like she should. She decides she needs to find herself again before her and Jim can be happy. 

Loosely based off of Grow As We Go by Ben Platt 

He was never meant to end up here, to meet her, and to have his life changed forever.

‘He’s not going to use her for a story. He’d known within seconds of seeing her sneak to that garden door like a lifeline, within seconds of slipping out after her, that he wasn’t going to do that.’

A series of Jim/Pam one-shots, inspired by lines in the show (now in chronological order!)  

The MTT Noobs finally figured out how to collab. 10 chapters of what occurred during the hiatus of S4. Answers to Jam's First Holidays together.

"It's not about ideologies anymore or what we wish the world was. It just isn’t. You have to decide what matters and then do whatever you can to keep it. Sometimes that means making impossible decisions; choices that take a piece of you.” 

So. There is an entire deleted B-Roll from "Sex Ed" where Pam and Jim are fighting all day, and then he slaps her butt on the way out. It's never explained. This is my explanation.