What should a married man do who committed adultery and aborted his fetus, and wants to atone for his sin, given that the woman he committed adultery with is evading marrying him?

You are advised to repent and fear Allah, and not to make this worldly life your greatest concern, but rather to turn towards the Hereafter. You must fear Allah concerning your wife and fulfill her rights, including maintenance and kind companionship, as the Prophet, peace and blessings of Allah be upon him, said: "A believing man should not hate a believing woman; if he dislikes one of her characteristics, he will be pleased with another."

If there is a need for a second wife, let her be a woman of religion, good character, and beauty. The woman mentioned is not suitable due to her bad character and lack of religiosity. If the woman is an apostate disbeliever from Islam, it is not permissible to marry her. If she is from the People of the Book, it is not permissible to marry her if she is not chaste.

The expiation for fornication is repentance with its conditions: ceasing the sin, regretting it, and resolving not to return to it. As for the blood money (diyah) and expiation for aborting a fetus, please consult specialized fatwas regarding that. When marrying a second wife, you must be just between the two wives in maintenance, companionship, and division of time.