So it's nice to hear that happiness isn't tempered by the built-in challenges of being in a super-high-profile relationship.
"It doesn't feel like a hardship," the star of HBO's The Leftovers said about being with Jennifer Aniston in the August issue of Details, featuring the solemn-faced actor-writer-artist on the cover. "It doesn't feel difficult."
But aren't the paparazzi, for lack of a better word, annoying?
"It can be an annoyance, but it's not the end of the world," Theroux told the magazine. "You have to center on what its core thing is, which is that you met someone you fell in love with. It's hard to explain. I just find myself wondering, What's the big f--king deal?"
Big f--king deal, indeed. Way to not let the madding crowd get you down, Justin!
As for the written words that tend to accompany all those paparazzi pictures in the tabloids, Jen's 42-year-old fiancé said that "it's always based on fiction."
"You just kind of ignore it," he continued, "but then you also become reluctant to say anything about the relationship. I could say everything's good, and then it's reflected back as 'JUSTIN THEROUX: EVERYTHING'S GOOD?' That just creates this echo chamber, and it ricochets around the internet, it just gets wacky."
But he and Aniston soldier on. And from our perspective, being with Theroux doesn't look like such a tough proposition either, at least based solely on his ripped physique.
The 42-year-old showed off the results of all that time he spends in the gym for Details as well, cutting an impressive shirtless figure, his six-pack abs and muscled arms rippling for the camera.
Theroux, who starred with Aniston in Wanderlust and now stars in a very dark cable series, playing a suburban sheriff who's trying to keep it together after 2 percent of the world's population inexplicably disappeared, also talked about transitioning between comedy and drama.
Or seeing the comedy in the drama.
"There are certain actors who can grab a woman by the back of her hair and plant a deep one on her and say something like ‘We gotta save the world,'" he intoned, "and that's not me. I can't not be outside of my body, making jokes about that dialogue. Some people do it really well and effectively because they have the charisma to pull that off. I just know that I don't."
Asked about not being the most recognizable face in the acting pack throughout most of his career, Theroux said that he honestly hasn't minded flying under the radar.
"There's a huge distinction between wanting to act and wanting to be a famous actor," the Washington, D.C., native and nephew of famed author Paul Theroux said.
"Most of the people that jump off buses in Hollywood just want to f--king ‘make it.' And I never had that drive. Honestly. I could never visualize myself in that way. To me it seemed so cart-before-the-horse-y.
"I still think a long, slow road is always the better road. Or at least for me it's been the better road."
(Something to remember for all those wondering when that wedding is going to happen.)