For nine seasons, The Office delivered comic stories about life at a failing paper company. There were pranks, Dundies, and arguably above all else, the fairy-tale romance of prank-happy salesman Jim Halpert (John Krasinski) and sweet receptionist-turned-office administrator Pam Beesly (Jenna Fischer). But what if it was all a lie? Many people who buy into The Office fan theories are pretty sure Jim stepped out on Pam, all while he looked like America’s sweetheart.
Cheating sitcom couples aren’t anything new, but for some ardent viewers of The Office, it’s hard to swallow the idea that Jim cheated on his super-crush after finally getting to be with her. Maybe after all those years of pining for Pam and a brief dalliance with Karen Filippelli (Rashida Jones), Jim grew bored and began having affairs. If hearing that Jim could've cheated on Pam is like getting an arrow through your heart, you may want to take a moment and sing some acapella to cheer yourself up between each of these depressing Jim and Pam fan theories.
The final episode of The Office explores the lives of the cast members after the documentary airs. PBS hosts a Q&A panel, and an audience member asks Pam why she stopped trusting Jim.
While Pam speaks vaguely and doesn't provide many details, Jim comes to her defense.
From Redditor /u/annyc:
Jim cuts her off. He awkwardly dances around what was going on, but says that it was his fault. He sort of implies that Pam was treated unfair in the editing and he was shown in a better light.
Pam also states during the Q and A that after nine years there are some things you just want to keep private. I think this is why, even when she and Jim are 'alone' during the finale she doesn't bring up the affair.
Some of the biggest drama of Season 8 is built around Cathy Simms (Lindsey Broad), a temp who takes over for Pam while she's on maternity leave, and who openly states her intentions to seduce Jim.
She makes her move when they're together on a business trip in Florida.
Cathy comes up with a story about bed bugs in her hotel room, prompting her to hang out with Jim. On camera, he pushes Cathy away and gets Dwight (Rainn Wilson) to bust up the whole thing. Jim comes out looking like a good guy and a faithful husband.
But what if that wasn't the end of it? Maybe, once the crew went to bed, Jim hooked up with Cathy.
From Redditor /u/Sarlax:
Everything we saw between those two was part of Jim's plan to have deniability.
In Season 9, Jim splits his time between Scranton and Philadelphia while working with Athlead, and his relationship with Pam is incredibly strained. But the documentary producers show very little of what Jim is doing.
Pam doesn’t seem like the kind of person who would be upset when her significant other chases his very attainable dream. Is something else going on?
From Redditor /u/annyc:
The Producers have chosen to show only things directly relating to his relationship with Pam. Why don't we meet any of his new coworkers? Perhaps because he's flirting with one of them?
As the series goes on, Jim grows increasingly impulsive.
In Season 1, he mostly pulls harmless pranks on Dwight. By the end of Season 2, he decides to move to Connecticut to work at a different branch of Dunder Mifflin. In the Season 7 episode "Classy Christmas," Jim smashes a snowball into Dwight's face just because of one comment and, later that season, he straight up walks out of a conversation with Erin (Ellie Kemper) because it "wasn't interesting."
If this is the kind of thing Jim is doing on camera, it's not out of the question that he could randomly hook up with someone at a bar one night after work.