Mandy Moore and Ryan Adams: Why They Split
01/29/2015 AT 02:10 PM EST
"They split forever ago," a source tells PEOPLE. "Their friends all knew."
Although Adams, 40, filed for divorce on Jan. 23, he lists the date of separation as Aug. 4, 2014, according to legal documents obtained by PEOPLE. (Moore, in documents filed earlier the same day, did not give a date of separation.)
"They honestly hadn't seen each other in forever," continues the source. "There came a point where they almost never did."
Moore, 30, was only 24 at the time the two quietly wed in March 2009, which may have played a role in their growing apart.
"She got married so young, and even though the age difference wasn't huge, it was still tough on the relationship," says the source.
More importantly, the musicians – who collaborated on Adams's self-titled album last year – just had very different personalities.
"They really were just two very different people," the source explains. "He's such an introvert, and she may not want her life out there every day, but she's so sweet and friendly and social. Total opposites."