What sin did the questioner commit in this marriage, and did she wrong the man's other wives by accepting to marry him, causing God to punish her with divorce, and did the husband wrong her by divorcing her?

A woman's work is impermissible if it involves khalwa (seclusion) or unlawful mixing with men. Furthermore, Islamic law does not condone a relationship that arises from camaraderie or friendship between a man and a non-mahram woman. As for your marriage to a married man, it is not an injustice to his wives, and there is no harm in a woman accepting it. Regarding a husband divorcing his wife, if it is for a valid reason, it is not an injustice. However, if it is without a valid reason, some scholars have deemed it forbidden. Divorce might also be better for both parties. Allah the Almighty says: "But if they separate [by divorce], Allah will enrich each [of them] from His abundance." (An-Nisa: 130).