“What the hell are you doing, Jack?”

Excellent question. It gets asked twice during the episode — and it could have been asked again and again throughout the heartbreaker of a finale.

Spoiler alert: Do not read until you’ve watched the season finale of “This Is Us,” titled “Moonshadow.”

In this episode — written by Isaac Aptaker and Elizabeth Berger (who’ve been elevated to co-showrunners for the second season), and directed by Ken Olin — we see a far darker side of Jack (Milo Ventimiglia). Whether in the distant past, before he met Rebecca (Mandy Moore), or in the ’90s, as a frustrated husband, he’s not the “perfect” character we’ve been idolizing all season long.

This is a man who drinks. Who fights. Who nearly commits robbery. Jack, what the hell are you doing?

Creator Dan Fogelman warned Variety that the finale was going to get dark, and indeed it did. The tension that had been building between Jack and Rebecca exploded in a massive, punch-to-the-gut fight — and ended with Rebecca telling Jack to pack his bags. “I think you should go stay with Miguel for a while,” she tells him. “Give us some air.”

But before he walks out the door, in true “This Is Us” fashion, he leaves her with one helluva heartbreaking speech: “You’re not just my great love story. You’re my big break and my love story. And I know it may not feel like it right now, but it’s just getting started.”

At least we did get some glimpses of hope: As Jack delivered his speech, promising that their kids were going to be OK, too, we saw Kate planning a singing career, Kevin pursuing a meeting with the director (with Sophie standing by) — and most poignant of all, Randall telling Beth he wants to adopt a baby.

So is this the beginning of the end for Jack and Rebecca? Or can this marriage be saved? Here, creator Dan Fogelman breaks down the finale — and what it means for Season 2. “I’m excited to see people react to it,” he says. “I’m excited to see audiences engage with it. It’ll be interesting.”

Well, you can’t say you didn’t warn us. You went dark.

I think hopefully for everybody it feels real. Even the best marriages have bumps in them. Every time we’ve gone into this storyline with Milo and Mandy, these characters in this timeline, it’s the reality of a long marriage that’s withstood a lot of different things in a lot of different stories in a lot of different time periods. I think it’s important that we’re going to leave the audience wondering and thinking and expose them to that side of the marriage as well. That’s always been part of the plan since the inception.

That moment when Rebecca wakes up the morning after the fight, looks outside her bedroom and realizes he wasn’t sleeping there broke my heart.

I know. Breaks my heart, too. I don’t even remember if that was in the initial script or that was something the director suggested. There’s also the moment at the end when you think you want Mandy to stop him (from walking out), for him to stop himself. It’s a marriage at a crossroads.

So where does this leave them? He gives a wonderfully impassioned speech about how she’s the love of his life. Does it win her over?

That’s the question on the table that will carry people over through the off-season. What’s next for these two? Is this a bump in the road? I think that’s the question of the show. There’s always been the dark times. Certainly this is one of them. But we operate from a place of optimism. The lines at the end and Mandy’s reaction to them, to me, if I’m an audience member, it’s a cliffhanger but there’s also a bit of hope. I think that would be a fair and comfortable place for the audience to be.

If my math is right, we’ve got to be getting closer to Jack’s death. Are they together when Jack dies?

I think that’s the question to be asking. I can’t give you the answer. But that is the question.

We’re seeing a Jack in the past that’s very different than the Jack we’ve come to know. 

The plan has always been that with Jack, we’ve created a bit of a modern-day superhero as a father and as a husband. Having seen glimpses of his background, that doesn’t necessarily grow out of nowhere. It comes from somewhere and there’s something that formed him. It would be overly simplified to say he’s always been exactly like this. In watching him at his most troubling time as a young man we still see the Jack and the good guy that he’s always been at his core. But we evolve as human beings. When we’re first meeting Jack as a 36-year-old guy with his children, he’s a different guy than he was a decade ago. He’s just back from war and having this tough spell and this tough upbringing. There’s part of us that we bury and this moment comes out a little bit. And we got a glimpse of it. We’ll get that eventually from all of our characters.

Should we give credit to Rebecca for saving him from himself, from committing a crime?

That’s the idea. It’s this sliding doors moment. I don’t think any of Jack’s behavior in his past is naturally inherent to him. He’s a good guy who’s just in a bad place. And is sick of having his a– handed to him by the world. He’s about to make this bad decision, probably the worst decision he’s ever made. And it’s almost as if destiny has put in front of him the woman who changes everything, who literally stops him in his tracks. I’ve always referred to Jack’s death as the hinge on which this entire family swings. For Jack, meeting Rebecca was probably the moment his life swung on. I think she saves him.

You said earlier that the season ended on a cliffhanger that set up an optimistic future. While that might not be true for Jack and Rebecca, that’s certainly true for the kids.

I was just speaking to Sterling about how interesting that storyline is going to be to explore for him and for Beth and their whole family. Even in the midst of that cliffhanger for Jack and Rebecca, the focal point of that final episode, we also have these final moments that are moving forward that are really exciting to write for, these uplifting things. Whether it be Randall and Beth going on this quest to maybe adopt a child, and Kate starting up this singing career and Kevin having these opportunities in his acting life, being in a position to what he’s hoping to accomplish in his romantic life. That’s where we’re going to pick up in season two. We’ll continue with those storylines.

And maybe Rebecca’s heart will melt?

I think yes. There’s a deep, deep gestating love between those two. Even though they had a monster fight, even though the fight churned up deep-seated character stuff, one fight is not necessarily going to be the end all and be all. It’s not like we’re going to come back in season 2 and they’re going to be divorced and dropping the kids off for the weekend. We’re not going that quick and that far. I think it’s fair to say there’s a journey ahead for these two, regardless of how they ended.

WATCH: ‘This Is Us’ Cast on How They Reacted to Jack’s Death