Olivier Martinez and Halle Berry "have been at odds for a long time."
The French actor, 49, and the Oscar winner, 49, both recently filed for divorce after two years of marriage, but their relationship has "been a roller coaster from the start."
A source said: "Olivier and Halle have been at odds for a long time. After a while, there was very little left to salvage.
"[They] spent a lot of time working on their marriage. It's been a roller coaster from the start."
While the pair had their issues, "things were starting to calm down" after they enjoyed "a nice summer together."
But the 'Extant' actress reportedly decided to finally pull the plug on their romance after an LAX airport employee recently filed a $5 million lawsuit against them, claiming the 'Dark Tide' actor allegedly shoved him to the ground with a baby carseat in January.
The source told PEOPLE magazine: "When she found out about the lawsuit, she was done."
Friends close to Olivier, who has two-year-old son Maceo with Halle, insist he was committed to their marriage until the very end.
One insider said: "Olivier loved being married. A divorce was never the plan."
The pair are eager to avoid a custody battle.
The insider added: "They want to work it out as loving parents so each can spend a lot of time with Maceo. He deserves that and more."