Is it permissible to marry another woman, with the approval of her guardian and witnesses, and with the intention of divorcing her later, knowing that the first wife does not wish to return and that the husband fears falling into sin?

The matter of marriage is serious, and it is imperative to consult scholars before proceeding with it. The mere consent of the guardian for the marriage is not sufficient; rather, the guardian or his representative must be present at the marriage ceremony. Similarly, witnesses are required to be present at the ceremony and to hear the offer and acceptance. If this did not occur, then it is a marriage without a guardian and without witnesses, and therefore it must be annulled. There is no sin upon you if you lived with this woman believing the marriage to be valid, and if children resulted from it, they are attributed to you due to the شبهة (doubt/semblance of validity). If there was an agreement to separate before the marriage contract, then it is a temporary marriage (Nikah Mut'ah), which is invalid by the consensus of jurists. If the wife refuses to reside with you in your country without a legitimate excuse, she is considered disobedient (nashiz). The expiation for sin is repentance.