Is it permissible to marry someone who has confessed to zina (fornication/adultery) and repented, or is it better to leave them?

The crucial factor is the suitor's current state. If he possesses good character and religious commitment, then agree to his proposal, based on the Prophet's (peace be upon him) saying: "If someone whose character and religious commitment you are pleased with comes to you, then marry him. If you do not do so, there will be tribulation on earth and widespread corruption." It is necessary to verify his current condition. If marriage is not feasible, then the relationship must be severed because he is a non-mahram. And whoever is afflicted with sins must repent and conceal their own faults.