Is the difficulty in getting married, despite the desire, ability, and search for a committed spouse, attributable to the supplication of an oppressor, and how can one repent and be saved from the evil of this supplication, and is there expiation for it?

Delayed marriage can be a trial that is met with patience, chastity, prayer, and exerting effort to find a righteous wife. Even if she is not perfect, accept one who observes her religious obligations and avoids major sins. If you have wronged anyone, hasten to repent and seek absolution from the wronged party. It is not necessary for a supplication made against you unjustly to be answered. You should ask Allah for well-being and give charity, for it repels affliction. If you are asking about a specific expiation for wrongdoing, there is no expiation for it except repentance and seeking absolution from the wronged party.