Ashlee Simpson: Pete Was Just Too 'Erratic'

2/9/2011 3:00 PM PST

Ashlee Simpson: Pete Wentz Was Just Too 'Erratic'

Ashlee Simpson filed for divorce because she can't handle Pete Wentz's crazy behavior ... sources connected with the couple tell TMZ.

TMZ just broke the story that Ashlee has filed for divorce.

Our sources say, no third party is involved.  One source very familiar with the situation tells TMZ, "It's really all about Pete's erratic behavior."  The source adds, "She really wanted out."

The divorce move is surprising -- just a few days ago they appeared to be one happy family during an outing in West Hollywood.