Their relationship 'went stale'. [=became dull or predictable]
She felt 'stale' [='bored'] in her job.
a room filled with 'stale' smoke
(..) Could I have one? A lemon one...or any of them. Three coppers. - How about a nice fat pigeon? - Oh, piss off now. Go on. Do you have any stale ones from yesterday? Or any burnt ones? Piss off! Hey, where's everyone going? What's happening? - They're taking him to the Sept of Baelor. (..)2011 TvShow: Game of Thrones Title: Baelor Season: 1 Episode 9