Drew Barrymore has made a "choice" to be happy.

After the 41-year-old actress confirmed her split from husband Will Kopelman last week, Good Housekeeping released an interview with the mother-of-two, where she reveals her struggle to stay positive. "I first loved Nan [Jimmy Fallon's wife, Nancy Juvonen] because she loved the word 'happiness' so much. But last year, I called her with tears in my eyes, going, 'Nan! I’ve finally figured it out! It's not the word 'happiness' that's so powerful. It's the word 'choice'!'" Barrymore recalls. "Happiness is not this yellow, blithe, floating thing. It's something that takes a tremendous amount of work."

WATCH: Drew Barrymore and Will Kopelman Release a Joint Statement One Day After Calling It Quits

The mother-of-two says "there's a warrior aspect to being happy," and insists "you've got to fight for it."

"And only when you've got that kind of earned happiness is it really good," she adds.

WATCH: Drew Barrymore Talks 'Hard Time' in First Post-Split Interview -- 'I Kind of Knew Life Was Heading in a New Direction'

No doubt Barrymore is leaning on her gal pals -- who she refers to as her "first family" -- after the breakup, and calls Cameron Diaz her "cozy friend."


Good Housekeeping

"If you are in scary prison in the middle of nowhere, call Cameron. She'll get you out. If you're looking for the best dinner-cooking partner and watching TV-on-the-couch friend, call her. If someone is in a medical situation, call her!" she quips. "We have incredible honesty with each other, and we work hard on our lives and our friendship."

MORE: Cameron Diaz Opens Up About Supporting Pal Drew Barrymore Following Split -- 'We Rely on Each Other'

As for her and Kopelman's two daughters, Olive, 3 and Frankie, 2, Barrymore says motherhood has shown her how to truly love someone. "I am who I am because of my daughters. I'm an overachiever parent, and not because I think I'm going to repeat the patterns of my parents. That's not my fear -- I've already broken that pattern in my life," she explains. "But having grown up in the opposite way, I'm raising my children with all consistency, all protection."

"This is my chance to get it right," Barrymore continues.

MORE: Drew Barrymore Split -- 7 Things She's Said About Love and the Challenges of Her Marriage

A source close to Barrymore revealed to ET how the estranged couple plans on moving forward post-split. "[Drew] really wanted to give her daughters a normal family life, and she will do everything to make sure they [have one]," the source shared. "They're on good terms and are trying to keep everything cordial for the sake of the girls. They'll keep their apartment they have on the Upper East Side [of New York City] for now. Olive is in school here [in NY], but also is enrolled in L.A. Drew was never really based full-time in NYC -- they were always back and forth."