Is the teacher's love and compassion for his students—who are the same age he was when he lost his father—considered a mistake?

You must fear Allah and beware of excessive love for youngsters, for it is from the footsteps of Satan. It is not permissible to look at beardless youths with lust, and scholars have agreed upon its prohibition, due to the Almighty's saying: "Tell the believing men to reduce [some] of their gaze and guard their private parts. That is purer for them. Indeed, Allah is Acquainted with what they do." You must rid yourself of this excessive love and make your love for them ordinary, for the sake of Allah. And hasten to marry, as the Prophet, peace and blessings be upon him, said: "O young men, whoever among you can afford to marry, let him do so, for it helps him lower his gaze and guard his modesty. And whoever is not able to marry, let him fast, for it will be a shield for him."