Michael Sheen allegedly felt "no need" to settle down with Rachel McAdams.
The 44-year-old British star and 34-year-old Canadian actress split in February after two years together.
Sources have now claimed the cause for their break-up was conflicting visions for their future.
"Rachel wants to settle down and is dreaming of having a family. Sheen always seemed content with their relationship," a source told People.
"Since he already has a daughter [Lily, 14, with actress Kate Beckinsale], he feels no need to have more children. He wants to focus on his career."
The source said the couple's parting was amicable. They realised neither would compromise on their future plans and so agreed to go their different ways.
Sheen and McAdams hope to keep in touch with each other but only on a friendly basis.
"They still have some contact and are friendly," the source said.
"They tried to work things out, but at the end they just couldn't agree. It caused some frustration and they thought it was better to go separate ways."
McAdams and Sheen met when they worked on Woody Allen's critically acclaimed movie Midnight in Paris in July 2010.
The couple took their relationship public in October of the same year.
It had been previously speculated that the long-distance aspect of their romance may have been the problem that caused their split.