Why would a woman threaten the side chick after tolerating cheating for years?

Why after 4 years of knowing the husband is cheating, would a wife start threatening the side and sending insults on social media.

Never once confronting their lying cheating husband that pursues this woman and reinforces their bond.

Financial dependence? He's mentally unstable or unsafe to handle divorce $$? Teenagers? The wife thinks the hisband is under a spell lol? I'm very perplexed at the psychodynamics of all this.

Why would a woman threaten the side chick after tolerating cheating for years?
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