The former cricketer was engaged to the 50-year-old actress for three years before they went their separate ways in 2013.
Speaking to The Times magazine Warne, 45, said, "Relationships are hard. Really hard. They shouldn't be, but they are. Tough. Always an interesting dinner conversation: are two people meant to be together for the rest of their lives?"
However, the couple struggled to find time to see each other due to their hectic careers, Warne insisted "scheduling" was not the only factor which led to their split.
"She was going to America, doing her breast cancer awareness stuff for Estee Lauder. I had my poker, I had cricket commentary. I had children in Australia, so just putting all that into the mix. The number of whiteboards we had about travelling," the former Australian cricket star explained.
"So the reason we split up, it wasn't just scheduling. It just shouldn't be that hard," he added.