How can one deal with a husband who is constantly abusive, uses foul language, repeatedly threatens divorce, and then demands kind treatment after all of that?

Excessive swearing is reprehensible, as Allah Almighty says: "And do not make [your oath by] Allah an impediment to your doing good" and "And do not obey every a Ḥallaaf (frequent swearer) and a Mahin (worthless)." The prohibition is further emphasized if the swearing involves divorce or by other than Allah, as the Prophet, peace and blessings be upon him, said: "Whoever swears an oath, let him swear by Allah or remain silent." If the harm caused by the husband to his wife is evident, such as verbal abuse and hurtful obscene language, the wife has the right to seek divorce. If the wife wishes to stay, she should advise her husband to refrain from ill-treatment and excessive swearing by divorce, and treat him with kindness and respect. If she does not wish to stay, she can refer the matter to the Sharia courts to seek a divorce.