Credit: Christopher Polk/Getty Images

After nearly three years, Ashlee Simpson-Wentz and Pete Wentz want out of their marriage.

"After careful consideration, we have made the difficult decision to file for divorce," a rep for the stars tells in a statement. 

"We remain friends and deeply committed and loving parents to our son Bronx, whose happiness and well-being remains our number one priority.  We ask that everyone honor our privacy as we navigate this next phase of our lives."

Citing "irreconcilable differences," Ashlee, 26, filed papers in an L.A. court Wednesday, documents at TMZ confirm.  In the filing, she asks for joint legal and primary physical custody of Bronx -- and seeks spousal and child support.

After embarking on a romance in late 2006, the singer and actress wed Fallout Boy rocker Wentz, 31, in May 2008 -- when she was about 3 months pregnant with their son Bronx, now 2.

"They've been unhappy," an insider close to the couple tells "They're living two separate lives."

Back in June 2009 -- just 13  months into their union -- Us Weekly reported serious friction and combative fights between the newlyweds, who struggled to adjust to their new roles as spouses and parents. "They fight constantly," a source told Us at the time. "She is seriously considering leaving him....They're in different places."