What is the ruling of Islamic law regarding parents' refusal to allow one of them to return to care for their only son who is suffering from tribulations, as well as their refusal to marry him off, under the pretext of building a future and academic excellence, knowing that the son fears deviance for himself?

If you can patiently abstain from fornication and complete your studies, that is preferable, as it combines honoring your parents with pursuing your education. If you cannot, then frankly inform your parents that you are unable to complete your studies without marriage. If they agree and assist you, that is what is desired. Otherwise, you are not obliged to obey them in this matter, as they would be commanding an act of disobedience. In such a case, you are permitted to marry without their consent, based on the Prophet's (peace be upon him) saying: "There is no obedience in disobedience to Allah; obedience is only in what is good." We advise you not to rush your decision, to seek the mediation of someone who can persuade them, to turn to Allah in prayer, and to consult people of wisdom and religious knowledge.