Memo to Nick Lachey: Vanessa Minnillo has marriage on the mind – and hand.

Pointing to a 5-carat ring on her middle finger, Minnillo, 28, tells Las Vegas columnist Robin Leach, “It will be 10 carats when it moves to the fourth finger!”

Leach says she was laughing when she said it. But in the course of a brief interview posted on his Vegas DeLuxe blog, Minnillo mentions marriage three times.

Noting that Lachey, 35, couldn’t make it to Vegas with her because he was at a friend’s birthday party, she pouted, “So once again it looks as if I’m always the bridesmaid but never the bride.”

Not that there’s a problem, she quickly adds. “This romance is still going strong,” she says. “There will always be rumblings and rumors that we’ve broken up, but in fact, it’s very much still on – and it keeps on getting better.”

So much so that, “Maybe this will be the one time I wind up the bride instead of the bridesmaid!”