Revenge should be left in God's hands. It's in the Bible, Romans 12:19, NIV. "Do not take revenge, my friends, but leave room for God's wrath, for it is written: 'It is Mine to avenge; I will repay,' says the Lord." Proverbs 20:22, NIV. "Do not say, 'Ill pay you back for this wrong!' Wait for the Lord, and He will deliver you."
We should resist revenge in favor of love. It's in the Bible, Matthew 5:38-39, TLB. "The law of Moses says, 'If a man gouges out another's eye, he must pay with his own eye. If a tooth gets knocked out, knock out the tooth of the one who did it.' But I say: Don't resist violence! If you are slapped on one cheek, turn the other too."
Do not be happy when your enemy stumbles. It's in the Bible, Proverbs 24:17-18, NIV. "Do not gloat when your enemy falls; when he stumbles, do not let your heart rejoice, or the Lord will see and disapprove and turn his wrath away from him."