What is the ruling on secret marriage? And what is the ruling on not being fair between wives, knowing that the second wife lives in a rented apartment, and her husband does not spend the night with her despite his financial ability, and she has no children?

A husband must be just between his wives in terms of division [of time], unless one of them waives her right. As for gifts, presents, and preferences in dowry, housing, or furniture, the husband is not required to be just in these matters. He may give to one wife without the knowledge of the others, as long as he fulfills each wife's rights and spends on her reasonably. He is not obligated to equalize spending and clothing if each wife is adequately provided for.