Pete Wentz has revealed his marriage to Ashlee Simpson collapsed after he had a drug relapse.

The Fall Out Boy rocker - who split from the 28-year-old singer in February 2011 after two and a half years of marriage - blames their divorce on his addiction to prescription drugs, including Xanax and Klonopin, and credits their four-year-old son Bronx for giving him a reason to seek help.

Pete Wentz's son constantly asks him crazy questions.

The Fall Out Boy rocker - who has joint custody of four-year-old Bronx with his ex-wife Ashlee Simpson - can't believe how quickly the little boy has grown up and revealed he recently started asking him ''400 questions a day'' about the world.

Ashlee Simpson is an ''awesome'' mother, according to her ex-husband Pete Wentz.

The Fall Out Boy rocker - who split from the 28-year-old singer in February 2011 after two and a half years of marriage - says the duo get along really well now because they are focused on co-parenting their four-year-old son Bronx.

Pete Wentz's son wants to ''punch'' his next birthday cake to prevent himself from growing up.

The Fall Out Boy bassist revealed four-year-old Bronx, who he had with ex-wife Ashlee Simpson, is so determined to remain forever young that he plans to ruin the sweet treat when he turns five in November with the hope it will stop him from aging - an idea that Pete finds ''genius''.