Is it permissible for the husband to demand the return of the Mahr (dowry), marriage expenses, and the wife’s gold due to the existence of messages and a previous relationship between the wife and another man, and her seclusion with him before marriage?

It is not permissible for the husband to take anything from his wife's mahr (dowry), as it is her right. The same applies to gold gifted to her. As for borrowed gold, it belongs to her family. If it is proven that the wife has communicated with a non-mahram (definition) man, it is recommended for the husband to divorce her. He may also refrain from divorcing her until she ransoms herself from him with money, due to the gravity of her sin and the fear of her corrupting his bed. It is not permissible for the husband to defame or expose his wife; rather, he must conceal her faults.