Although Holly attended Hef's annual blowout at the Playboy Mansion last week, she spent Halloween in Sin City with her new man at the gala opening of his new show, Believe.
Holly departed Sunday, but it seems Hef's former best girl just can't get enough of Criss. "She left to go back to L.A. but is coming back Tuesday to spend some more time with him," a source tells E! News.
And expect Holly to rack up even more frequent-flier miles. She says herself this new romance will require weekly trips to Sin City.
—Reporting by Whitney English