Does a betrothed woman, whose marriage contract has been written, become forbidden to her fiancé and divorced from him if he asks her, "Do you accept to be unlawful for me if there was something in your past that does not please me and you hid it from me," and she agrees, intending to reassure him?

You were right not to tell your husband about your past sins, for it is not permissible for you to inform him of them, nor is he entitled to question you about them. Your husband's statement, "Do you accept to be unlawful for me if there was something in your past that displeases me, and you concealed it from me..." does not entail anything, even if he intended divorce, because it is merely a question about your acceptance, and he did not definitively declare you unlawful. Your acceptance or non-acceptance of divorce is not given consideration, because it is not an option (takhyeer), unlike if he were to say: "You are unlawful or become unlawful to me if you concealed something from your past that displeases me, and he intended divorce," in which case you would be divorced. We advise you to hasten the completion of the marriage to avoid obstacles.