"Diana and I have ended our relationship. However, we are committed to working together to raise our daughter in a healthy and happy environment," Martinez tells PEOPLE exclusively.
The actor and Dancing with the Stars champ, 30, posted a message to his Facebook page Wednesday touching on the difficulties of accepting change.
"People change [it's] a part of life, but sometimes [it's] easier to hold on to the memories of who they were rather [than] to realize who they have become…" he wrote.
The Iraq war vet met Gonzalez-Jones in 2008, when he joined the cast of All My Children while she was working as an assistant to the show's executive producer. The pair started out as friends, but took their relationship to the next level four years ago.
"All this time I was looking for the perfect guy, and I had him right next to me," Gonzalez-Jones told PEOPLE in 2011. "We were so good as friends that romantically, we just clicked right away."
A month after Martinez clinched the mirror ball trophy on ABC's hit reality show, he and Gonzalez-Jones announced that they were expecting.
Martinez was thrilled to become a father in May 2012, telling PEOPLE, "I kiss her non-stop all day long," adding that his daughter's nursery "is the best room in the house."
Reporting by CHARLOTTE TRIGGS