"It's quite a complicated relationship," he said. "It's not on, it's not off, it's somewhere in the middle. I don't know if I will ever get married, but I am happy."
Cowell, 52, met Hussainy in 2003 when she worked as a makeup artist on American Idol. They got engaged in February 2010.
The X Factor judge says he and Hussainy have not seen each other in a month but "are still incredibly close."