Will the husband be sinful if he informs the husband of the woman who intrudes on his life and whom he has repeatedly tried to convince to end the irrational relationship, after he previously had a relationship with her with the intention of marriage?

This tribulation is one of the most harmful trials for men. A Muslim must flee from such a woman as he would flee from a lion, because she harms his religion, his heart, and his morals. He must be firm with her and threaten to inform her husband. If she stops pursuing him, he should conceal her fault. Otherwise, there is no harm in using a means to prevent her, such as informing her family (father or brother). As for the woman, her action is a betrayal of her husband and her religion, and she must repent to Allah.