What should a young man do who wishes to propose to a girl he loves and fears falling into temptation, while his family objects to his marriage now because of his studies, which will take another four years?

If you wish to keep yourself chaste, then marriage is the most upright path. It is also a commandment of the Prophet, peace and blessings be upon him, who said: "O young men, whoever among you can afford to marry, let him do so, for it helps lower the gaze and guard one's chastity." The obligation of marriage becomes even more certain if you are capable of it and fear falling into indecency, at which point it becomes a fard (an individual obligation) upon you. Since you do not suffer from financial impediments, you should take the initiative to marry. If your family objects, using your studies as an excuse, you can opt to perform the marriage contract only and delay the consummation until you finish your studies, while attempting to convince them; their approval is not a condition for the validity of the contract.