Their relationship 'went stale'. [=became dull or predictable]
She felt 'stale' [='bored'] in her job.
a room filled with 'stale' smoke
(..) I'll do it. You'll do what? I'll kill him... first chance I get. Pi'a colada? More like stale bubblegum. Does anyone actually want their car to smell like the bottom of a sixth-grader's desk? Okay. Hemp? Really? (..)2011 TvShow: Breaking Bad Title: Problem Dog Season: 4 Episode 7