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

This Is Us traveled to San Francisco for KaToby — and the trip proved that the couple's marriage was anything but golden.

Tuesday's episode titled "The Hill," directed by Mandy Moore and co-written by Chrissy Metz, Casey Johnson and David Windsor, was the second episode of season 6's Big Three trilogy, focused on Kate (Metz) making a big step forward in her life. After a disastrous Thanksgiving with her family, Kate and Toby (Chris Sullivan) finally got to have quality time without their kids in the Bay Area, where he has been happily working at a startup.

Despite a few moments of feeling reconnected, it quickly became obvious that both Kate and Toby wanted different things for their future. Mainly, Toby wanted Kate, Jack Jr. and Hailey to move to S.F., where he thinks he can provide a better life for them financially. He even found a house for them, without consulting her.

Meanwhile, Kate was holding onto the memory of who Toby used to be when they first met at an Overeater's Anonymous meeting — the old Toby she fell in love with. Though she feels happy and fulfilled with her teaching job at the Music School for the Blind, the one thing that is making her unhappy is the rocky state of her marriage. Ultimately, fans know that KaToby is not endgame as a flashforward in the season 5 finale saw Kate getting married to music school boss Phillip (Chris Geere).

Below, Metz tells PEOPLE all about the episode she co-wrote and breaks down the unraveling of Kate and Toby's relationship.

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PEOPLE: How was working with first-time director Mandy Moore?

CHRISSY METZ: It was super exciting. I mean, luckily we've had a really nice friendship that we've cultivated over all these years in playing mother-daughter. There's always been this mutual respect but it was really nice because she understands these characters better than any other director who's just coming in. She was just so kind, sweet and patient, and had a vision. So easy and effortless, it was really nice.

Speaking of Mandy, her character Rebecca's speech at the cabin makes an impact on the Big Three in different ways. Kate was chosen as the backup captain after primary caregiver Miguel (Jon Huertas). What does that do for her going forward?

I think that she and Rebecca always had a bit of a bumpy relationship. It's unfortunate when Rebecca receives her diagnosis and she is starting to understand her mom through being a mother herself. There are all these revelations that they're having. It's just so nice that Kate feels validated. Even though her mom always felt as if Kate was her best friend, Kate didn't always feel that. So it was really sweet to see Kate understand for the first time that she is somebody that people, and her mother included, can rely on. She can be the captain as you said and she can really handle what's going on.

Rebecca choosing Kate really bolstered her confidence but also this understanding of who she's really become and that her mom might have seen it before she did, which I think is even more beautiful. That was a huge turning point for her and Kate actually choosing herself in a real way she had been trying to for many, many years. But when she realizes that Toby might not have been honest with her and there are all these other irons in the fire that she had no idea about, she's like, "Wait. What about me?" Yeah, the bittersweet nature of all of it is that they both are deserving of being happy. It just so happens that it's looking like together is not where they find their happiness any longer. It's all very complicated and layered but also very important for their evolution.

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As much fun as it was to see Chris in old Toby gear with the hair and the bright outfit, it was sad to know that's the version of him Kate held on to. Why bring back old Toby now?

Of course, she misses that part of her life and who Toby was to her. I think everybody loves the beginning of relationships, the honeymoon phase, because it is the fun part. We always tend to remember all the good and we forget to play the whole tape. I think old Toby for Kate is like her playing the old tape of this is all the things that I fell in love with him about. But at the same time, when he starts to make fun of Toby's clothes I think she realizes, "Oh, it's fun to commiserate with her subconscious," which old Toby is for her. She also has this understanding that she loves this person and he might have changed but he's not a bad person.

She just wishes that things were different and things were the way they were. Even though she knows deep down that it's not the right way because he was obviously very miserable, unhappy and stuffing down a lot of things. But it's complicated because he also went through a weight loss that he didn't really tell her about. She has all of these… not that she's building a case but she has all these ideas swirling in her head about who he is. Who she wanted him to be, who he is now and where does she fit in his life? Where does he fit into her life? It was great to see old Toby and Chris obviously did such a great job of that. I think she thought it was going to bring her comfort and it really just brought her to an understanding of the Bandaid she didn't want to rip off.

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Both Kate and Toby are happy and found purpose in their respective careers, though they're living in separate cities. Neither of them did anything completely wrong, they're just in different places in their lives, figuratively and literally. Is that something you wanted to focus on as a co-writer of this episode?

That's the whole point. Neither one of them is right and neither one of them is wrong. They're just moving in different directions and sometimes you move together and sometimes you move separately. I think it's really important to show the dissolution of a relationship in the most honest, real and relatable way. These are two people that love each other very much and they're really trying hard in every way that they know what they feel is best to keep this relationship going. Unfortunately, it's not ultimately what each other wants. They want separate things.

Did Kate and Toby succeed in trying to save their marriage or did they just realize that they're better off on separate paths of life?

They both are trying desperately and that's something really beautiful to witness but I think they're going to keep trying. If you love something you don't give up on it. I think they both love each other, but are we going to keep seeing them have the same fight? The same disagreement? The same argument? Ultimately, I don't know if it's able to be salvaged. They're going to, well I know they're going to continue to try, but things are not going to be easy for them.

What does the phone call to Phillip at the top of the hill mean?

She's ready to put herself first. If he gets to do what he wants to do, which means staying in San Francisco and having his own life, she wants to stay in L.A. and have the career that she's always dreamt of. She's very happy and so why can't both exist? That's the whole point is that they tried to let both exist and it was just too difficult. So we'll see.

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Previously you hinted about drawing inspiration from your own divorce, what specifically inspired this script?

I pulled some feelings of my real-life divorce. My ex-husband and I were like crying signing our divorce paperwork because we loved each other as people but we knew that we weren't supposed to be together. Many people, I think, have experienced that. The hardest part is holding onto something that you know is not meant for you. You feel like, "Oh well, I'm supposed to. What if I don't find anything better?" All of those feelings, I have personally gone through in my life. Unfortunately, you know intuitively when something isn't working anymore even though it's very hard to admit it to yourself.

You do love somebody, but it doesn't mean that they're your forever person. As the show always does, it teaches us how to get through hard stuff in our life. When we see somebody in pain or hurting and never choosing themselves that choosing yourself doesn't always make everybody else happy. That to me is something that I'm learning in my life. I'm really glad that was so beautifully orchestrated because it's really hard to choose yourself in a very real way. Kate never did that and there are many times where I haven't done that in my life. I think many people haven't. I love that she could do that by putting herself first, bolstering her confidence, and also not having to apologize for it or justify it. I don't think that's something that we're taught as human beings, especially women. That was important.

After the Randall-centric trilogy episode next week, the Big Green Egg will appear at Rebecca and Miguel's party. Is there anything you can tease about specifically how the Big Green Egg factors into the end of Kate and Toby?

Well, there's something aside from the Egg that occurs. Let's just say, it is not a normal party. I don't know if the Pearsons can have a normal party, if I'm honest. S--- always seems to hit the fan with the parties. When three or more Pearsons are gathered, s--- hits the fan. I think it's because there's a lot going on under the surface — resentments and stuff that goes on. There's a particular incident that happens between Kate and Toby and Jack that really solidifies their decision of not moving forward.

Was co-writing this episode the bittersweet part of finishing This Is Us? Were you able to accomplish what you dreamt of with this show? Not only with acting and singing on the show, but also now co-writing?

I mean I feel very content with where Kate began and where she is now. Who I am as a person and who I was before. Having all these incredible opportunities, just really stretching my abilities, just showing up for myself. I mean, that's half the battle, if not more. It's just really nice to be in a position where there's enough respect and collaborative desire to want to make the show the best it can be. I'm so grateful and very content. Do I want one more season? Probably, but you know, that's okay. We always want what we can't have.

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