Is informing the family about the fiancé's deception regarding providing a residential apartment for marriage, after the fiancée requested to keep the matter a secret, considered a disclosure of a secret and a betrayal of trust that necessitates expiation?

It is not obligatory for the husband to own a dwelling; rather, he must provide a suitable and independent dwelling for his wife, whether it is rented or loaned. Divulging a secret is impermissible and considered a betrayal of trust, unless there is an overriding benefit in divulging it or an apparent harm in concealing it. If you divulged the woman's secret for an overriding benefit, there is no sin. Otherwise, you have betrayed the trust, and you must repent to Allah. There is no expiation for you except repentance.