This song is about cheating.
She's found out he cheated on her and now she letting him know that he can't have her back. She's hating on him and ask rhettorically asking him questions about his new girlfriend and comparing it back to when they're were together. She's basically saying, there's no chance... they're shattered glass cos after glass shatters no matter how much you try, you can never have a whole glass again. and that's them!
This song is about cheating. She's found out he cheated on her and now she letting him know that he can't have her back. She's hating on him and ask rhettorically asking him questions about his new girlfriend and comparing it back to when they're were together. She's basically saying, there's no chance... they're shattered glass cos after glass shatters no matter how much you try, you can never have a whole glass again. and that's them!