[Warning: Major spoilers ahead for Justified's, "Alive Day."]

The jig is up for Justified's Ava (Joelle Carter) ... only she doesn't know it yet.

Ava has struggled in her role as a (reluctant) informant all season, and while it looked like Katherine Hale (Mary Steenburgen) might be the one to out her, it was Ava's own reckless decision to make a run for it in last week's episode that did her in. Fresh off encountering Ava before she was brought back home, Limehouse (Mykelti Williamson) called Boyd (Walton Goggins) to tell him that his fiancée was working behind his back with Raylan (Timothy Olyphant).

Boyd has never had it particularly easy, but the news is the latest in a string of things going very bad for him. "Last season was very, very dark for Boyd," Goggins told The Hollywood Reporter. "I think by the end of the season, with the killing of the older man for Ava and her protection in jail, it was the straw that broke the camel's back. It was just, 'I have to get out of this.' He knows the writing's on the wall, and what the writers did with that eloquent speech [in the season premiere to Dewey], that he was able to articulate about those times and those dreams and those aspirations were for different people … it was painful, but it was time; it needed to happen. It harkens back to what happened in season one when Boyd made the decision to let him go … by Boyd's standards, Dewey needed to die in season one. It was obviously a smart decision [by the writers] since Damon Herriman (Dewey) is such an incredible actor, to have Boyd spare his life. To have that come full circle in a way was bittersweet, but important to tell our story."

"[After that] for the first time since season two, Boyd felt it was like him against the world," he continued. "There was no allegiance. I think that plays itself out until he allows himself to believe in Ava again [this year], and the love he has for her. And turns himself over to this vulnerability. As smart as Boyd Crowder is, I think he's a fool. At least a fool for love. And that may be his undoing."

Read more 'Justified' Postmortem: Boss, Star on the Final Season Premiere's Brutal Twist

As fans saw in the final (silent) moments of "Alive Day," the awareness of Ava's betrayal is a devastating blow to Boyd. "I think there are two things that for a person in the world like Boyd that are detrimental to his fragile state of mind: the fear of dying in a mine is first and foremost one of his greatest fears," Goggins said. "You can cut him, you can shoot him, you can do anything you want to do as long as it's above ground. But the man has a genuine fear of dying in a mind, which I think is not unlike a lot of people who come from that part of the country. That is the bogeyman."

"[The second] is breaking his heart. Boyd Crowder with a broken heart is one of the most dangerous things I've ever seen for any character I've ever played," he continued. "He's a man who doesn't let anyone or anything in, ever. The man won't walk out of the house without his shirt buttoned at the top and the sleeve buttoned all the way down. For him to open his heart and love the way that he loves — this is a man who feels everything very deeply, whether you see it or whether you don't see it, he does. I know, I was in his shoes. And he feels for this woman in that way. It's devastating. It's almost irrecoverable."

Boyd won't sit idly by with this information, and in next week's hour, he takes an oblivious Ava on a hunting trip.

"It is one of the most volatile, mind-bending experiences I've ever had as an actor," Goggins shared. "It's psychological warfare, administered by Boyd Crowder. He's as nefarious and deviant as they come in a lot of ways. And a warning to the person who breaks his heart or puts him in that position, because he will put you through it until he finds out what it is he's looking for. Going through it was excruciating. It was very difficult to do. But so rewarding. It gets dark in the room before anyone turns on the light."

But is all hope lost for Boyd and Ava? "I think people underestimate Boyd's capacity for understanding and forgiveness when it comes to ways of the heart," Goggins teased.

Less likely to get any of that forgiveness? Zachariah (Jeff Fahey), whom viewers learned set a trap for Boyd — and who was willing to kill to make sure his intentions weren't revealed.

"It's so interesting for me as a fan of the show — I'm not around for people when they do their scenes," Goggins said. "I'm just there for what Boyd does, and I tend not to read those parts of the scripts when they come out, because I don't want to know. Especially this year. I really doesn't want to be affected by the words I read on a page about what's [going on] with Ava and Raylan. But if you look at it, Boyd is a man from the very beginning of the show, who knows more than anyone in a room. Chapters ahead of anyone else, except for Raylan. And sometimes it goes back and forth and he may be a sentence ahead of Raylan or a sentence behind Raylan. But this year, he doesn't see it. He doesn't see the betrayal by Ava. He doesn't see Zachariah until something glaring happens. He doesn't see the things around him because he's so focused on one thing: one last big score in order to leave a life that is not surrounded by violence."

"I equate Boyd's journey to a dude slinging rock in Harlan, or a guy mixing up oxycontin in his basement in a rural part of this country — how do you get out?" he continued. "What do you have to do? Is it education? And that works for a lot of people, when they get those opportunities. But in Boyd's case, when you're raised in a culture of violence, that's all you know, and that's what you fall back on. For him, it is a deep, deep desire to rise out of that violent adolescence poverty, that restricted small-mindedness that keeps him going. He's just trying to break the ceiling to get to some fresh air, because he's been breathing stale air his whole life. And it's so interesting to me as being a part of the show to be like, 'Don't you f---ing see? Can't you see? They're right there!' But he doesn't. And it'll be really interesting to see how that plays out. And what are the [lines] Boyd has to cross over. What is the point of no return this season in his pursuit for that goal, and how will he pay for that?"

For Goggins — who wrapped his work on the FX series last week and is filming Quentin Tarantino's Hateful Eight — shooting the final episode of Justified was a roller coaster of emotions. "I feel like we did 13 episodes in [shooting the finale] from an emotional standpoint," he acknowledged. "It was much harder than I anticipated it being, having been around that lap before with The Shield … it's so bittersweet. But I'm proud of it. I think we're all proud of it."

"There was such finality [from the start] in that moment [of losing Dewey]," he continued. "And then you say goodbye to directors who come and go with every episode, and actors who come and go, and you don't know from script-to-script if it's going to be you … I got to see a lot of people have their last goodbye, and that takes its toll on you. You know, eventually, you're going to be the person at the center of attention, giving that speech, and what are you going to say?"

Read more 'Justified's' Graham Yost Previews Final Season, Talks Pressure of Ending a Serialized Show

And while Justified creator Graham Yost was open about the ending being very much up in the air, Goggins shared that he was a part of the conversation about Boyd's ultimate fate for a bit of time.

"It's been an ongoing conversation for a long time," he said. "This season, at the very beginning … we had a conversation, all of the people who needed to be there about what they were thinking. Some of those decisions were outside what I was hoping for for Boyd, but as it turned out, it was the right decision. But I don't think Graham landed — and we didn't land as the voices of these characters — on exactly what was going to be said or how it was going to go down until the day of [shooting]. The story was in place, and Graham knew what he wanted, and the writers knew what they wanted. And I knew to a degree what I wanted, and Tim knew what we wanted, and it was still fluid on the day. This show has always been by committee, with one strong leader, and that is Graham Yost. He is not insecure in a way [that would prevent] making it a collaborative process; it's always been that, for both Tim and I. That's a rare gift, to be able to invite your two leads to sit at the table that way. And in doing that, it has made it trying at times, but I think we have a better product because of it. No one's coming from ego; it's all about trying to live up to the elephant in the room, which is Elmore Leonard. Graham and Tim keep us honest on the Elmore front, and I try and keep us honest on the serialized, kind of darker heart front. That's how it came down. But I think the fates conspired to be something that is satisfying to us, the creative counterparts. I just hope the audience likes it. It is what it is. I think it spoke to us. I think Graham was right making the decision he made."

Justified airs Tuesdays at 10 p.m. on FX. What did you think about Boyd finding out Ava's secret?

Twitter: @MarisaRoffman