Gwyneth Paltrow and Chris Martin reportedly clashed over her practice of Kabbalah.
The Hollywood couple - who have two children, Apple, nine, and seven-year-old Moses - announced their separation on Tuesday after working on saving their marriage for "well over a year", but it's claimed their relationship has been on the rocks for at least five years since Gwyneth began following the religion in 2009.
A source said: "Chris wasn't happy about it. He felt that he was starting to lose the woman he fell in love with."
Gwyneth and Chris began leading separate lives over the last couple of years as the 41-year-old actress became more and more enveloped in her Goop lifestyle brand and Chris, 37, began recording the latest Coldplay record.
The source told The Sun newspaper: "Chris is laid-back and low-key, and found it harder and harder to live up to her perfect standards.
"Gwyneth was focusing less on her showbiz career and more on her lifestyle projects.
"She also didn't feel like she got enough attention from Chris."
It's thought Chris even moved out of the family's Â£7 million ($11.6 million) home in London's Belsize Park last year and began living in Coldplay colleague Guy Berryman's small flat in Hampstead Heath, North West London.
The insider claimed: "Chris was really struggling with Gwyneth. Their relationship was under huge strain and he was doing everything he could to patch things up. But he felt he had no choice but to move out. Guy offered him a place to stay where he could hide out and deal with it all."