Is it permissible to supplicate for the annulment of a marriage after the عقد (marriage contract has been concluded), and what is the way to regain closeness to Allah after feeling that prayers for choosing a life partner have not been answered?

The guardian of a young woman should marry her off if a suitable match of good character and religious commitment proposes to her, in accordance with the Prophet's (peace be upon him) recommendation. This is a matter of recommendation, not obligation. A woman has the right to seek divorce (khul') from her husband if she dislikes him and fears she will not be able to observe God's limits with him. It is advisable not to rush into khul' and to pray that God facilitates what is good. Remember that faith waxes and wanes, and the remedy for spiritual lassitude is to hold fast to God, supplicate Him, strive for good companionship, and avoid bad company.