Is it forbidden for a wife to imagine another man while having intercourse with her husband?

Love and affection are not prerequisites for a stable marital life; rather, it is built upon living together kindly and upholding Allah's boundaries. You have done well in obeying your husband regarding intimacy, even with aversion, as long as you do not show it or fall short in his rights. However, imagining another man during intimacy is not permissible. You should seek the reasons for your lack of love for your husband and be open with him about them, while exercising patience and overlooking some matters, and looking at the good aspects of his character. This is in accordance with the Prophet's (peace be upon him) saying: "A believing man should not hate a believing woman. If he dislikes one of her characteristics, he will be pleased with another." Be sure to show him affection and love, even if it is forced, and cooperate with him in obeying Allah, while seeking Allah's help and making supplication.