"We were seeing each other for a while," Duff tells the magazine. "People don't know the ins and outs of everything. It was definitely my first more serious relationship since my ex-husband [Mike Comrie]."
"I was like, 'F**k it. He's my boyfriend,'" she said about her decision to go public. "I just needed to make sure it was right. People don't need to know my business until I really know my business, you know?"
Though Duff admits their personal relationship affected their professional relationship.
"He's like, 'You don't listen to me anymore! I give up!'" she shares. "I have a different trainer now."
As for if her ex-husband knew about Walsh, Duff says she and Comrie -- who share a 4-year-old son, Luca, together -- always tell each other when they start dating someone.
"We feel like it's respectful to keep everybody in the loop," she explains. "I don't know as much about his life as he knows about mine because mine's a lot more public."