'I Want to Be the Father Of Her Children'

John Cena says his life's been a wreck ever since his fiancee, Nikki Bella, dumped him before their wedding ... and says he'll do whatever it takes to get her back -- including having children.

"I had my heart broken out of nowhere," Cena said to Kathie Lee and Hoda on the "Today" show ... "I still love Nicole."

Cena says he was blindsided by the breakup -- and blames it on an "unfortunate set of circumstances" ... though he wouldn't elaborate on the specifics.

Cena says he's been depressed -- and he's been reflecting a lot ... and has decided to change his stance on fundamental things in order to make the relationship work.

"I love her. I want to be with her. I want to make her my wife. I want to be the father of her children. I just want us to work."

Cena has been pretty vocal about the fact he didn't want kids -- but says he's a changed man now.