The Rock of Ages actress was worried that her relationship with the American Idol presenter wouldn't work because of his huge success.
She told InStyle: "I was reluctant because he is such an influential guy, and what if it didn't work out?
"Our first date, I was so nervous that I just sat there and interviewed him with questions like, 'Are you loyal?' and 'Are you close to your family?'"
The pair met in 2007 when she worked on Dancing with the Stars and Seacrest's music talent show set was across the hall.
She added that Seacrest has changed her for the better.
Hough said about the 37-year-old host: "When we do see each other, we are super excited and do these cute and romantic things.
"I'm 20lbs heavier than I was when we started dating. And now we always have great wine, and I can tell the difference. So I told him, 'You ruined my life because I can't go to a friend's house and drink cheap wine anymore'."