What is the ruling of Islamic law regarding a woman marrying another man while still married to her absent husband, who refuses to divorce her or grant her a Khul', despite her need for marriage and the deterioration of her relationship with her husband?

A marriage that fulfills the conditions of validity is sound, and if it is so, then you have become a wife and it is your right that your husband should not be absent from you for more than six months except with your permission. It is advisable to seek the help of some virtuous individuals from your family or his family to negotiate with him, so that he either takes you to live with him or does not prolong his absence. If he responds, then praise be to Allah. If not, then it is advisable for him to grant you a divorce. If he refuses, then raise your case to the Sharia court to remove the harm from you. It is not permissible for you to marry as long as you are still married to this man, based on the verse: "and married women," referring to those who have husbands. We advise you to fear Allah and be patient, and beware of causes of temptation, and occupy your time with what benefits you. It is not permissible for you to allow any young man to speak with you about marriage, nor is it permissible for him to do so. Proposing to a married woman is more forbidden than proposing to a woman in her 'iddah, and if he does that, it is considered incitement (takhbib), which is prohibited.