The 41-year-old actress, who got engaged to Leob in 2012, announced the split with a screen shot of a note on her Who Say account, reported People magazine.
"Not that anyone should care, but in order to not give the press the chance to invent crazy and hurtful drama, I prefer to tell my fans personally that Nick and I have (decided) to be apart," Vergara said.
"We have (been) having too many problems with figuring out how to spend time together and (because) of my work and now his, its been getting worse and worse, not fun anymore," she added.
Already a mother to son Manolo, Vergara had been open about having a baby with Loeb, turning to a fertility doctor for help in expanding her family.
The former couple was last photographed together at the 2014 Golden Globes.