"I think if you are in a one- or two-year relationship, love is enough. You can thrive on that," the Monster Oscar winner, 32, tells Glamour for its July issue.
But, adds Theron, "when you hit years three and four, you realize that if you're going to live with somebody ... you have to be nurtured emotionally and spiritually, and you have to be intrigued. Because if that intrigue runs out, you're not going to want to go home anymore."
As for why Townsend is the special one for her, Theron says, "He's got beautiful feet and hands."
Only what if he should feel a seven-year itch? "I've always said that I worry about being with a man who doesn't flirt," she says. "I love that Stuart can watch tennis and tell me that he's got a crush on a tennis player. We're not meant to just like one person. But [that] doesn't mean you go and build a life with another person."
Echoing her previous sentiments, Theron, who costars with Will Smith in the upcoming Hancock, notes she is not ready for marriage. "Even when I was a little girl I never dreamed of the white dress and all of that," she says.
"I want to be clear: I am not judgmental about [the institution of] marriage. I am judgmental about how our government doesn't want to see the reality of gay and lesbian marriages."