Is it dangerous when an ex-wife says ‘if I can’t have you, no one can’?

My brother just underwent a divorce just last Sept but luckily there aren't any kids involved.

His ex wife has been recently leaving angry messages about how he'll pay for eveything and "If I can't have you, no one can, no one". They divorced because of her irrational jealousy. There is more. He just recently admitted that she also used to throw objects around the house, would block the exit door with her body when he wanted to leave and slapped him at times during arguments. That literally sounds like the definition of a controlling, abuser. She used to call him frequently, asking where he is.

There was a time he used to be in a bad mood with his parents and I. He also would rarely visit us. Now we now the truth. All I know is if a man were that controlling, did everything she did and say "If I can't have you, no one will" after a divorce, it would be terrifying? But we're now worried. Is a woman saying those nasty messages just as dangerous too?

Updates
3 h
She followed him once at his workplace. His manager caught her standing there but she left when caught.
Is it dangerous when an ex-wife says ‘if I can’t have you, no one can’?
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