This Is Us ' Chris Sullivan Breaks Down Kate and Toby's Explosive Fight — and Why It Was 'Scary'

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This Is Us fans have fallen in love with Kate and Toby's romance over the years. But as the series nears its end, with just seven episodes left, KaToby shippers will be heartbroken to find out what exactly led to their divorce.

Tuesday's episode, titled "Saturday in the Park," followed the Pearson family in Los Angeles at Miguel (Jon Huertas) and Rebecca's (Mandy Moore) 10th-anniversary barbeque that highlighted Toby's (Chris Sullivan) much-hyped Big Green Egg smoker. While he and Kate (Chrissy Metz) played party hosts, their marital issues were also at the center as arguments from the couple's San Francisco trip lingered. And cracks in their marriage weren't the only things at the forefront.

The Damon house's ceiling literally cracked due to the plumbing issues that were long put off and temporarily patched up before Toby moved up north for his new job. The anniversary party was spoiled by water leaks and KaToby conflicts only escalated everyone's stress. During the plumbing kerfuffle, Kate and Toby's son, Jack Jr. (Johnny Kincaid), who looked forward to Saturdays in the neighborhood park but had to skip the favorite outing due to his parents hosting the barbeque, accidentally snuck out of the unlocked house. The blind toddler safely made it to the park on his own but had a scary fall, which resulted in a nasty cut on his forehead and a trip to the hospital for stitches. Thankfully, grandma Rebecca, who is dealing with onset Alzheimer's, found Jack Jr. after she remembered her previous conversation with her grandson about how much he enjoyed muddy puddles in his red rain boots at the park.

After the family returned from the hospital, Kate and Toby exchanged verbal blows outside their house about who was in the wrong and their differing parenting methods with their unsighted child's "limitations." Furthermore, Kate brings up their long-distance issues and how she doesn't want to uproot her and her kids' life from L.A. Meanwhile, Toby stood firm on his preference to permanently live in the Bay Area where he believes he can best provide for them and they can stay a family.

Below, Sullivan breaks down the episode and tells PEOPLE about the tension between Kate and Toby that exploded in front of her family on what was supposed to be a celebratory day.

"The pain that each individual person experiences in their life can be an opportunity for fracture and growth. It all depends on how that is processed and how it is responded to," the actor teases of the fight's impact on Kate and Toby.

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PEOPLE: When you got the script about the argument that you and Chrissy have outside the house, before Kevin (Justin Hartley) and Randall (Sterling K. Brown) come into the scene to aid her, were you like, "Oh boy, this is going to be a lot."

CHRIS SULLIVAN: Yeah. I mean just to realize like, "Oh, this is going to be a long night." It's one thing for Chrissy and me to process the end of this relationship together on screen, but then to have the two brothers show up — it was scary. It was scary to stand on the front lawn having it out with Chrissy, and then to have these two very powerful, strong men show up. It was a lot.

For Toby, was he finally able to express how he's been really feeling? Did all that pent-up frustration come out in that fight?

I think the biggest problem in Kate and Toby's relationship has been their inability to process their fear and their sadness in a healthy way. Screaming about it on the front lawn is still not the best way to do that, but at least now it's out. It's one of those things where... it's one of those bells that you can't un-ring, but it needed to be rung. It needed to be said.

RELATED: This Is Us' Sterling K. Brown Teases How Kate and Toby's Marital Issues Affect Pearson Family BBQ

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Toby has been a part of the Pearson family for a while now. The fight ends with what looks to be the Big Three versus Toby. Does Toby realize he was never really a part of the family or he's always secondary to the family?

That's one of the ongoing themes about the beneficial side of a family forming a protective circle around itself and the isolating side of a family forming a protective circle around itself. Letting people in, but not too far. I mean, ask Beth if she feels like a member of the family. Ask Miguel if he truly feels like a member of the family. I guess it just depends on the day. Honestly, it depends on the current climate of the Pearson family. [laughs] It has its benefits and it has its detractors.

Is it all downhill from here for KaToby?

I don't imagine it getting much worse. I mean, of course, I know if it gets worse or not [laughs], but we know that the relationship ends. I guess that's the only answer.

RELATED: This Is Us' Chrissy Metz on Co-Writing the 'Dissolution of' KaToby in the 'Most Honest Way'

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There's been a long buildup to this fight and what happens to Kate and Toby, especially knowing that Kate is remarried in the future. But it was especially heartbreaking because it was at times told through Jack Jr.'s point of view with the fights he overheard and understanding why the park is "where Mommy and Daddy are happy." For you as a parent in real life, what were those scenes like to act out? (Sullivan and his wife Rachel welcomed their first child, son Bear, in July 2020.)

They're painful. Part of the thing that you see in the TV show is, and that you see a lot in TV and film, is parents arguing in front of their children. The thing that — as Rachel and I start to investigate healthy ways to parent and all of the different methods — doesn't get shown, or the thing that needs to happen in my research is, if you're going to have a disagreement or fight in front of your children, you also need to have a resolution in front of your children so that they see that that's how that works. It's not just a fight and then all of a sudden magically everything's fine because you've made up in the other room.

That's one of the ways that this show is really helpful for me because I can see these things and can be like, "Oh, this is really uncomfortable. I definitely don't want to do this. This is not the way." We can kind of get out in front of stuff like that. Rachel and I can connect and be like, "We agree, we don't want to do this, this way. Right?" And be prepared for stuff like that.

RELATED: This Is Us Explores Realities of Being a Parent — and Sets Up Big Changes for the Pearson Family

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In a previous flashforward, Jack Jr., now a well-known musician, has a smoker of his own and he said that the Big Green Egg was the symbol of the end of his parents' relationship. We find out how he got the scar on his face — it wasn't due to the smoker. What does he mean when he called it the symbol?

It was the centerpiece of the day. It was the symbol, it was supposed to be something that brought everyone together. There are these symbols in our lives, and we think that there are easy fixes. Or "if we can just go on this vacation." Or "if we can just get rid of this credit card debt." Whatever the thing is that we think is going to fix everything. Toby has this idea that he's constantly chasing this Jack Pearson ideal of grand gestures and unifying the family. It doesn't always work out that way. The Green Egg, although it is not personally responsible as the fine people at Green Egg Smokers are glad to find out, it represents a day when things really began to fall apart.

RELATED: This Is Us' Jon Huertas on Miguel and Rebecca's 'Taboo Moment,' Teases How They Find 'True Love'

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As the show comes to a close, do you have your eye on something you want to take? Or is there something that you have already taken as a memento to remind you of your time on This Is Us?

I can't take it because it would be grand theft auto, but I've asked the producers and the powers that be if I could purchase the Pearsons' Grand Wagoneer. My wife and I have always loved those cars and that one's in good shape. It kind of is a symbol of that family and the journey the show's been on.

I mean, what are they going to do with it? The studio, sometimes, they hold onto these things. They park it in storage, it sits, it rots and it doesn't work. I mean, the museum of television isn't going to put a whole car in there. I will love it, use it, honor it and take care of it. I think that's what it deserves.

At PaleyFest, Mandy said she threw up after reading the script for the second to last episode and Chrissy said she got emotional. What was your reaction or have you even read it yet?

I haven't read it yet. I've been having a hard time reading the episodes this season. I read them, kind of, at the last minute before we go work on them, because I just, I don't know, I don't want it to be over. ... I would do one more season.

This Is Us airs Tuesdays at 9 p.m. ET on NBC.

This interview has been edited and condensed for clarity and length.