Drew Barrymore 'Really Bummed' Over Split From Will Kopelman: New Details Revealed

A source close to the 'Miss You Already' actress tells ET why the former couple called it quits.

Drew Barrymore and Will Kopelman really did try to make their marriage a lasting one.

Less than a week after the 41-year-old Miss You Already actress called it quits from her art consultant husband after more than three years of marriage, ET has learned new details on what led to the split -- and how they plan to move forward -- from a source close to Barrymore.

WATCH: Drew Barrymore and Will Kopelman Split

"Drew is really bummed that it didn't work out," the source revealed. "They really tried hard towards the end to make it work, but they decided going their separate ways was best."

According to the source, Barrymore became extremely close to Kopelman's family including her sister-in-law, Jill Kargman -- the writer, creator and star of Bravo's Odd Mom Out -- when the two resided with Kopelman's parents, Arie and Coco, in New York City during the beginning of their relationship. The two started dating in early 2011 and said "I do" at Barrymore's Montecito, California, estate in June 2012.

"[Will's family] became her own," the source said. "I think it filled the void in her life of not having [a family] of her own. At the end, I think she felt worst about leaving them, more so than Will."

Last December, Barrymore was a guest on the Happier with Gretchen Rubin podcast, where she couldn't stop gushing over Kopelman's family and how "extraordinary" it felt to have good in-laws.

"My sister -- who is a sister-in-law but we just dropped the 'in-law' -- I love her so much," she said. "I hit the in-law jackpot. And she's the same, it's like sister-in-law jackpot."

"It binds you in a different way," she continued. "This new chapter of blood family, in-laws, this new glue. It's extraordinary and it's like nothing I've ever known. It's amazing."

And while Barrymore's relationship with her in-laws is certainly on her mind, there's another post-marriage factor that trumps all -- her children. ET's source also touched on how Barrymore and Kopelman feel in regard to how their divorce will affect their two daughters, Olive, 3, and Frankie, 1.

NEWS: Cameron Diaz Opens Up About Supporting Pal Drew Barrymore Following 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 explained. "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."

On Monday, Barrymore gave her first interview since the split, where she admitted that she "kind of knew" her life was "heading in a new direction."

"I had a really hard time a couple of months ago," she told PopSugar. "I called someone that I really trust, respect, and believe in, because he has always been the conductor of grace. I said, 'What's your advice?' And he said, 'You put one foot in front of the other.'"

WATCH: Drew Barrymore Talks 'Hard Time' in First Post-Split Interview

ET previously reported that talk of a separation between Barrymore and Kopelman had been going on since October 2015, though no papers had been filed at the time.

To hear more details on the breakup, watch the video below.