Why do people get jealous? Also, how can I protect myself from nazar (evil eye)?
Humans have a natural tendency to feel unhappy when they see someone who enjoys blessings much greater than they enjoy themselves. Some people are not pious enough to fight this tendency, so they feel a strong desire for the blessed person to lose the blessing and wish bad things to happen to them.
The evil eye is not mentioned in the Quran, so I do not consider it important enough to be worth worrying about. The best protection would be to read the Quran daily. Chapter 113 of the Quran contains a prayer against envious people, so you can try to memorize it and recite it when you feel any worry about envy and the evil eye:
Say, “I take refuge with the Lord of Daybreak.
From the evil of what He created.
And from the evil of the darkness as it gathers.
And from the evil of those who practice sorcery.
And from the evil of an envious when he envies.”