"He's devastated. Nobody intends to go down this path," a source tells PEOPLE. "They both battled, and he really battled to try and save the marriage but ultimately it was the best thing for the kids and for him and Jen."
Announcing their divorce on Tuesday, Affleck, 42, and Garner, 43, made it clear that parenting their three kids, Violet, 9, Seraphina, 6, and Samuel, 3, will remain a top priority. Both plan to live on the couple's 8,800-sq-ft property in Los Angeles for the time being.
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"They've been separated for 10 months but he was living at the house," adds the source, noting the two are also using a mediator to ease the division of their assets. "These are things that they have consciously done because they want to make sure that this is as easy as they can make it on the kids."
While rumors of trouble had dogged the couple – fueled recently by moving trucks seen at their home during a long-planned renovation – the two had been in years of therapy, says the source. "These are two people who really tried to save their marriage and worked really hard at it," the source adds. "Ultimately they had grown apart and they did what was best for their kids."
Reporting by LIZ McNEIL