01/29/2009 AT 04:00 PM EST
doesn't need a piece of paper to make her love for Liev Schreiber official.
"We're very much together," the actress, 40, tells Parade
magazine. "We just don't have that certificate, and that's OK with both of us."
The couple, who welcomed
their second son, Samuel Kai, in December and have an 18-month-old son, Alexander Pete, may one day "just wake up and go, 'Hey, let's do this," Watts says, "And maybe not. He and I have a family."
Though Schreiber, 41, gave her "a beautiful ring," Watts – who described her longtime partner as "a complicated man, which I've always been drawn towards" and "fiercely intelligent" – says they're not rushing into anything just yet.
"It's not like I've grown up having this dream of a fairy-tale wedding," she says. "My mother married twice and had two divorces. And Liev comes from the same kind of background."
While she doesn't divulge more details about their relationship, Watts opens up about her ex-boyfriend, Heath Ledger
, whom she met in 2002 while making the film Ned Kelly
, by noting that his eyes "would tell a thousand stories in one glance."
"It's still incredibly difficult," she says about Ledger's death from an accidental drug overdose
in January 2008.
"There was a wonderful mixture of power and fragility at work in everything he did, which just pulls you in, she adds. "His strength didn't scare you. It intrigued you. And his fragility touched you."
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