How can a woman who does not wear a hijab start wearing it, despite her fear that this might lead to her husband's decreased interest in her, his neglect of her, and his attraction to other women?

The legal headscarf (hijab) is an obligation established by the Qur'an, the Sunnah, and the consensus of the Muslim nation (Ummah), due to its role in promoting chastity, modesty, and safeguarding women. It stands in contrast to the immodest display (tabarruj) of the جاهلية (pre-Islamic era of ignorance). Adhering to Allah's command brings goodness, and hearts are in Allah's hand; He turns them as He wills. Obedience to Allah brings Allah's love and people's love. The husband must fear Allah and encourage his wife to wear the hijab before the Day of Regret.