Why don’t women who unknowingly get involved with a married/taken man tell the wife/girlfriend when they find out?

I found out yesterday that my fiancé cheated. According to the cell phone messages, the other woman found out about me via social media and he blocked him. However, she did not bother to tell me despite finding my social media.
Why don’t women who unknowingly get involved with a married/taken man tell the wife/girlfriend when they find out?
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