Chris Sullivan Has a Message for This Is Us Fans After Katoby's Emotional Split

"It's over, Toby," Kate (Chrissy Metz) says during the most pivotal scene of This Is Us Season 6, Episode 12 (the show's 100th episode). "It's time." 

Metz's delivery here is quiet and somber, like she's been thinking these words for a while but was too afraid to say them. This declaration comes after an explosive fight she has with Toby (Chris Sullivan)—a fight where Toby screams that he's unhappy whenever Kate's in the room. A fight where Kate criticizes Toby's parenting skills for the umpteenth time. A fight that's interrupted by their toddler son, Jack, who put his toy in the toilet to try and stop his parents' arguing. 

That last bit is devastating for Toby specifically, who vowed to never let his children be exposed to the domestic squabbling he witnessed as a child. But this fight with Kate was exactly that. It was mean, it was loud, and as fans know, it was inevitable. 

Season 6, Episode 12 actualized the dissolution of Toby and Kate's marriage, something This Is Us has been building up to for a while now. As Metz tells NBC Insider, there wasn't one incident that caused the breakup. "It's been little cuts, and then you finally bleed out," she says. Those cuts include strain brought on by Toby's long-distance job, disagreements about what to feed their children (and how to raise them), plus dishonesties on Toby's end. The most recent one? That Toby was offered—and turned down—a job in Los Angeles, which would've solved their long-distance issue.

This new episode saw Katoby attempt to fix their marriage. Toby takes the job in L.A., and they start couples' therapy—but everything seems too far gone. They keep having the same fights, and their resentment only builds. Things hit a fever pitch at a one-on-one dinner, where a comment about baby Hailey's bedtime leads to a full-out brawl. That's when Kate sadly relents, "It's over." 

After they sign their divorce papers, Kate and Toby have a moment of levity in an elevator. Whitney Houston's "I Will Always Love You" starts playing—an on-the-nose soundtrack to their current situation that sends them into hysterics. But the laughs are short-lived: Before they leave each other, Toby says that he'll "never see" why their marriage had to end. 

Eventually, Toby eats those words. He meets someone new and, of course, we know Kate ends up with her boss, Phillip, played by Chris Geere. (Episode 12 explores Kate and Phillip's relationship progression, as well, and more is coming.) A flash-forward shows Kate and Toby both older, happily with other people, and enjoying their grown-up, soon-to-be-famous son Jack's singing. Right before the episode ends, we pan back to Kate and Phillip's wedding day, where Toby calls her and says something beautiful: "I want you to know that I see it now." Translation: He sees why their marriage had to end. 

That last scene, in a nutshell, sums up Sullivan's advice to fans mourning the end of Katoby. "Everything's 'gonna be OK," he tells NBC Insider, and Season 6, Episode 12 proves this. "That's what this show is about. From the first episode, they show you tragedy and pain, but they also shoot you into the future and show you, 'Oh, this family's OK.' We jump back and forth and see, 'Oh my gosh, this father died in a fire.'  Then, we jump forward and see, 'Oh, this family's OK.' Tragedy and joy are held in both hands." 

He continues, "When you’re experiencing joy, you think that it's never 'gonna end. So when something [bad] comes along, you think, 'Oh, why me? I was just up here!' But everything cycles around." 

Indeed, it does. This Is Us airs Tuesdays at 9 p.m. ET on NBC. Catch up now on NBC.com.