Pete Wentz on Ashlee Simpson Divorce: 'I Thought It Was a Forever Thing'

Pete Wentz is getting super-honest about his highly publicized 2011 split from Ashlee Simpson.

The two were married for almost three years after tying the knot in 2008, and have one son together, six-year-old Bronx Mowgli.

"I thought it was a forever thing," the 35-year-old Fall Out Boy rocker says about their relationship in a candid new interview with Howard Stern. "I'm not the kind of guy ... My parents have been married, I think, 35 years. Forty years, this year, maybe? But no, I didn't [anticipate the split]. At the same time, we were both very young."

VIDEO: 8 Couples Who Renewed Their Vows and Still Split

He reveals he hit a personal low point after Fall Out Boy went on a break in 2013 -- which definitely contributed to the demise of their marriage.

"Here's what it really was: At 31, we'd had all these great years, you know, as a band, and then we took time off, and I basically became Mr. Mom," he explains. "I had the beard, the flannel shirt. I didn't know what my identity was. That factored in. When your identity is what you do, it's hard when you stop doing it."

"I think when you stop caring about your personal appearance, your personal hygiene, it makes you even more depressed, but it makes you do it more," he adds. "It's like a vicious cycle."

One particular incident that's telling of his state of mind at the time is when he hosted a Jingle Ball event, and very clearly wasn't into it.

"I went and I hosted some Jingle Ball thing, and I was really upset with being there," he admits. "I wanted to be performing but I wasn't performing. I drank a bunch of beers and that night, I banged my head and I ended up needing to get stitches. All this stuff that was not like myself at all, it was part of this cycle of being bummed out."

Wentz counts his depression as just one of the many factors that contributed to the split.

"I think it was a combination of all these factors at once, including being too young," he says. "I think there's an important thing where you know how to fight, because you can fight with somebody and it's not the end of everything. But if you don't know how to have those arguments, then they become nuclear."

But he does admit to initially feeling some resentment at Simpson, for what Stern calls breaking up with him at his "low point."

"I would be an idiot to think that I didn't contribute to the unraveling of it," he now reflects. "Of course, at first, I'm like, 'This sucks! You bailed on me!' That kind of stuff. But you get perspective. We have a kid together. Our kid is awesome."

Bronx remains the two's number one priority. Wentz reveals that he and Simpson have a 50/50 custody agreement.

"We've actually figured out how to parent that way in a really good, healthy way," he says. "And, we can be friends."

Both Wentz and Simpson have since moved on from their failed marriage. Simpson married Hunger Games star Evan Ross in August, and is reportedly expecting their first child together. The "Centuries" lyricist welcomed his son, Saint Laszlo, with his girlfriend, model Meagan Camper, also in August.

"To me, the right way is when we have time to plan it," he says about his future plans to marry Camper. "I didn't really want to do it in the public eye this time. I didn't really want to do it in magazines. We're just doing it on our own a little bit."

"I do still believe in marriage," he clarifies. "My parents are married. My sister is married ... I'm a man in love!"

VIDEO: Ashlee Simpson's 'SNL' Lip Sync Fail 10 Years Later

Check out the video below to hear all about Wentz's adorable son Saint Laszlo!