With a hot new movie, We're the Millers (in theaters August 7), and a wedding on the way, Glamour's September-issue cover star Jennifer Aniston opens up about her hang-ups, her hopes, and her hard-won happiness. To read the full interview and see all the photos from our cover shoot, download the digital edition now or pick a copy of Glamour on newsstands August 6. Jason Sudeikis: One of the nice things about this movie—and we have now done three together—is that in this one we have a child. "In the movie, your character is learning to access her parental instincts," the former Saturday Night Live actor, who is engaged to Olivia Wilde, told Aniston. "I would argue women are better at that."  Jennifer Aniston Hints at Brad Pitt Years: I Needed "Therapy" 
 
 If Jennifer Aniston could go back it time, it sounds like she'd do a few things differently during her five-year marriage to Brad Pitt. I know Justin, for instance, has extremely amazing paternal instincts," she said of her fiance of nearly one year. "Because [growing up] he had to sort of become the parent. I think when you have to become the parent when you're a younger person, you learn those instincts." "I noticed on set that you had very maternal instincts with [costar] Emma Roberts," Sudeikis noted. "I did," Aniston agreed. "But she's wise beyond her years." "And, you know, we already feel married," she added. Still, the actress added that she's had those mama instincts "all throughout my life." Jennifer: Well, that was because I felt so strongly about it, when I heard what she was going through. Jason: And they took what she said out of context. In the September issue of Glamour, the 44-year-old actress has a frank discussion with her We're the Millers costar, Jason Sudeikis, about how she wishes she would have gone to therapy in her thirties, but why she's finally happy with fiance Justin Theroux. PHOTOS: Jen and Justin's matching style 
 
 Aniston also opened up what advice she'd give herself in her thirties. Go to therapy. Clean up all of the s--t. Clean up all of the toxins and the noise," Aniston said. "Understand who you are. Educate yourself on the self." Jennifer: [But] you can undo a lot of things. If you're not happy, you can become happy. Happiness is a choice. That's the thing I really feel. Like with friends who refuse to get happy, who refuse to rise above the discomfort of where they're at." PHOTOS: Jennifer Aniston's Us Weekly covers 
 
 "It's almost like your character Rose from We're the Millers," Sudeikis said of Aniston's stripper character. "'This is all I deserve' kind of thinking. It's like, no, you deserve— 
 
 Jennifer: You actually deserve to have a family. "And once you meet yourself, and truly love yourself, then you attract that. And look -- I mean, the two of us have found these two, beautiful, loving, open people." "We have a similar timeline," Sudeikis told his costar. "We both went through the same thing. I mean, I would hear you talk about [guys you were dating], and I'd be like, 'Oh, f--k. I don't want to be like that to somebody else.'" "Yeah. And look how far we've come!" "High five!"
– What advice would Jennifer Aniston give to her 30-year-old self? "Go to therapy. Clean up all of the s--t. Clean up all of the toxins and the noise. Understand who you are. Educate yourself on the self," she says in a new Glamour interview. Why is this interesting? Because, as Us points out, when Jen was in her thirties, she just so happened to be married to Brad Pitt. More from the interview, which was actually carried out by Aniston's We're the Millers co-star Jason Sudeikis: On fiance Justin Theroux: "Justin ... has extremely amazing paternal instincts. Because [growing up] he had to sort of become the parent. I think when you have to become the parent when you're a younger person, you learn those instincts." The advice she'd give her teenage self: "Don't try so hard. Pay attention. Do your homework. Go to class." And her 20-year-old self: "Not to fret so much. I did OK in my twenties." And more on her thirties: "You can undo a lot of things. If you're not happy, you can become happy. Happiness is a choice. ... You actually deserve to have a family. And once you meet yourself, and truly love yourself, then you attract that. And look—I mean, the two of us have found these two, beautiful, loving, open people." In another recent interview, Aniston told the AP she and Theroux "already feel married." She shot down recent rumors of pre-wedding jitters and said they simply haven't tied the knot yet because "we just want to do it when it's perfect, and we're not rushed, and no one is rushing from a job or rushing to a job."