What is the secret behind the feeling of comfort and tranquility when staying away from a woman on public transportation, and the feeling of inner conflict and the desire to enjoy looking and touching on other occasions?

Clarifying the impermissibility of a man sitting next to a non-mahram woman, and the tranquility found in abandoning the forbidden, is part of the reward for obeying Allah. One who is sincere in abandoning forbidden things will not find difficulty after the initial moment. As for inner conflict and the desire to sin, these are from the whispers of Satan and the commanding self that inclines to evil, and one must seek refuge in Allah from them and strive against the self. To protect the heart from evil thoughts, one must know that Allah is aware of hearts, and feel shyness before Him, and venerate Him, and fear Him, and prefer Him above all else, and dread the consequences of those thoughts that destroy faith, and know that they are a trap of Satan, and that they cannot coexist with faith in one heart, and that they are a shoreless sea that drowns the heart, and they are the valley of fools that yields nothing but regret.