How can a committed young man who suffers from the whispers of Satan during his solitude remain steadfast on the path of righteousness and occupy his free time with what prevents him from falling into sins?

The fear of Allah, constant awareness of Him, and shyness before Him protect a servant from error; this is the station of Ihsan (excellence). One must beware of being among those who hide from people but do not hide from Allah. Sins committed in private are from the whispers of Satan and the soul that incites evil. One must hasten to repentance and seek forgiveness, and not despair, for Allah forgives sins. The important thing is that the servant does not persist in the sin, that his evil deed grieves him, and that he follows a bad deed with a good one to erase it. The calamity lies in continuing to commit sins without repentance, which causes rust (or stain) on the heart.