On Wednesday, the couple announced that they were divorcing after almost three years of marriage.
Wentz's reported custody plans come into conflict with Simpson's. She is reportedly seeking primary physical custody of Bronx with visitation for Wentz.
An insider close to the pair claimed that Simpson decided to end the marriage because of Wentz's "erratic" behaviour.
"It's really all about Pete's erratic behaviour. She really wanted out," the source told TMZ.
However, friends of Wentz have denied the allegations and said that the couple simply grew apart.
"After Bronx was born Ashlee made a conscious decision to get out of the business, but Pete's heart was in music so he kept touring and that became a big issue in their relationship," said a second source.