She 'shacked up' with her boyfriend.
an old 'shack' in the woods
young couples 'shacking up'
(..) they came and ruined it. I know, I know. Look, they can't see us... we can't see them. We're aII aIone in this IittIe shack. ActuaIIy, you know what? It's kind of cozy in here... and there's no one I'd rather be here with than you. ReaIIy? (..)2001 The Princess Diaries