Is it permissible to supplicate against the former fiancée's wife and her husband after the wife engaged in insults and defamation, knowing that I tried to avoid contact with the husband and defended his wife?

If the situation is as you have described, then it is not permissible for the woman to insult or expose you, nor for the suitor to incite her to do so. You are permitted to supplicate against them to the extent of the injustice inflicted upon you, but patience and refraining from supplication are better. The Messenger of Allah, peace and blessings be upon him, said: "Whoever supplicates against the one who wronged him has indeed triumphed." Your speaking with the suitor without a valid need is an injustice to yourself; you must repent, and a suitor is a stranger to his fiancée until the marriage contract is concluded.