The 36-year-old Oscar-nominee told EOnline.com: "Sometimes when someone [in the press] asks me about my dating status, I get really quiet about that because I want to protect it.
"When I'm engaged someday - who knows to who - I'll probably be more open about it.
"Seeing all these interviews with actors talking about loves of their lives and then they break up in a year and you're thinking, 'What if something happens and they end up being a total jerk?' Then you forever have these pictures of you standing on the red carpets together."
'The Help' star, who was first spotted kissing and hugging her boyfriend when they made a rare public appearance together at the Women in Film 6th annual Pre-Oscar Cocktail Party in February, previously revealed she would hate to be in a relationship with another actor.
She said: "I have a rule. I don't date actors, so he's not in the business, at all. ... He's in the fashion industry."
She also explained why she wants to keep her relationships private, saying: "In this business it's very tough to maintain a relationship because we're like gypsies -- always on the move. And the more you share your relationship with the world the less special it becomes. So I always try to keep my dating life quiet."