Ashlee Simpson-Pete Wentz Divorce: Amicable, But Her Call

Don't expect a bitter fallout between Ashlee Simpson and Pete Wentz, who filed for divorce Tuesday. But sources also say it was not entirely mutual.

"It's very amicable. They're on very friendly terms and speaking – it's fine," a source close to the couple tells People. "They've just grown apart."

"They've been growing apart for quite some time."

Ashlee and Pete married in mid-2008. [Photo: Pacific Coast News]

Maybe so, but Wentz is getting divorced against his will, sources close to him tell TMZ, adding that he absolutely did not want to end the marriage.

Wentz tried talking Ashlee out of filing divorce papers, to no avail. She wanted out of the marriage, possibly due to the rocker's "erratic behavior."

Still, they're putting on a civil, united front for now.

"It's all about [2-year-old son] Bronx. They're fantastic parents – Pete says she's a great mom, and she says he's a great father," says the source.

"It's about Bronx's care and well-being and happiness."

There was no third party involved, but Simpson, 26, and Wentz, 31 – who has been touring with his new band Black Cards – are both emotional.

"It's a sad ending to something that was promising," says the source. "They're each trying to figure out what this transition is going to be like."