"For Kit, being an addict, it's very important for him to recognise himself as such," The Good Fight alum, 35, said in the cover story for Harper's Bazaar UK's June 2022 issue.
She added, "The AA community has provided such a loving space for him to feel heard, to make sure he's not alone. But if it weren't for rehab, he would be in a very different headspace right now."
Leslie said she is "doing well," noting that Harington, 35, suffered from addiction in 2019, "so we're now several years into his sobriety."
Added Leslie: "I've learnt a lot about addiction and it's something Kit is forever going to be aware of, but it's on him whether he chooses to drink again. No amount of nannying is going to be able to stop him from doing what he decides to do... I don't choose to put that pressure on myself. The responsibility of his behaviour is on him. It's not on me to guard him from it."
According to Harper's Bazaar UK, the two bought a second property in Suffolk, where they planned to go after Harington finished performances of Henry V at Donmar Warehouse in London.
"We're going to make a home, try to make friends. We're just going to use our son!" she joked of their 14-month-old baby boy. "In London, we're firing on all cylinders, and when we get to the countryside, we can just turn it all off."
Harrington first opened up about his battle with addiction in August, telling The Sunday Times that he "went through some pretty horrible stuff" after Game of Thrones ended in 2019.
"Things that have happened to me since Thrones ended, and that were happening during Thrones, were of a pretty traumatic nature and they did include alcohol," he said.
RELATED VIDEO: Ireland Baldwin Reveals Shame Over Alcohol, Substance Abuse: 'Didn't Talk to My Parents for a Year'
"You get to a place where you feel like you are a bad person, you feel like you are a shameful person. And you feel that there's no way out, that's just who you are. And getting sober is the process of going, 'No, I can change,' " Harington continued.
"One of my favourite things I learnt recently is that the expression 'a leopard doesn't change its spots' is completely false: that a leopard actually does change its spots. I just think that's the most beautiful thing. It really helped. That was something I kind of clung to; the idea that I could make this huge fundamental change in who I was and how I went about my life."
He previously checked into the Privé-Swiss retreat in Connecticut back in May 2019, stating that he was treated for "mainly alcohol" during his stay. "Kit has decided to utilize this break in his schedule as an opportunity to spend some time at a wellness retreat to work on some personal issues," Harington's rep told PEOPLE at the time.
The Eternals actor also discussed the toll it took on his marriage to Game of Thrones costar Leslie, with whom he tied the knot in June 2018 in Scotland. "You can imagine the stresses that it causes to those around you," he explained.
"I will say about my addictions that I kept them very, very quiet and I was incredibly secretive and incredibly locked up with them," Harington added. "So they came as quite a surprise to the people around me. Which is quite often the case, I guess."
If you or someone you know is struggling with substance abuse, please contact the SAMHSA helpline at 1-800-662-HELP.