Is it obligatory to inform a suitor about a fiancée's previous relationships, or should one conceal them?

A Muslim must shield his Muslim sister and it is not permissible to disclose what he knows about her affairs except by allusion, as much as needed for sincere advice. If your friend consults you, this becomes obligatory. You should advise your friend with the counsel of the Messenger of Allah, peace and blessings be upon him, that a woman is married for four things: her wealth, her lineage, her beauty, and her religion, and that the best provision in this world is a righteous woman, without implicitly disparaging the aforementioned girl. It is important to note the prohibition of establishing friendly and affectionate relationships between the sexes.