02/25/2014 at 11:00 AM EST
Paula Patton and Robin Thicke's decision to separate
came as a surprise, in part because they seemed to be a fun-loving couple on red carpets – including at the Grammy Awards
But signs of trouble in their marriage may have started as early as 2010, when the couple welcomed their first child
The "Blurred Lines" singer, who was spotted out at Disneyland with their son on Sunday, also said that they were having a problem finding balance. "It was hard when we became parents, because we had to balance our careers with this new person in our lives," Thicke told PEOPLE
at Art Basel in 2011.
"[Having a baby] changed everything," he added. "It was tough at first. She was stressed. I took time off. I lost my mojo. After a while, we hit our rhythm and we are more in love and supportive than ever."
Both Patton, 38, and Thicke, 36, have seen their careers blossom since becoming parents, and an industry source says their grueling work schedules may have been a factor in their separation.
"They're both at the top of their careers right now and they're never together. She's filming in Canada and he's on tour," says the source.
Cheating rumors have also plagued the couple. Thicke was photographed grabbing a woman's backside at N.Y.C nightclub 1Oak following his controversial performance
with Miley Cyrus
at the MTV Video Music Awards in August
"He didn't act married," says an observer.
Still, the couple has nothing but love for one another. Says an insider: "They do love each other. They'll continue to be friends."
For more on their split, pick up this week's issue of
PEOPLE magazine on stands Friday.
Reporting by K.C. BAKER, MARY MARGARET and LINDA MARX