Why I feel an urge to take revenge?

He cheated with me. He act with me as a true lover, though he had his problematic wife. She was having affair with some other guy. I loved this man with pure love. Honestly. He just cheated me and went to his wife. I didn't even understood. He used to lend money from me, as he was in financial crisis. But he didn't returned me all of my money. When I asked for it. He refused to give it to me. He is living with his wife. I tried to forget about him totally. For the last 3 months, I didn't even think of him. But recently as I heard from one of my friends that he is living with his wife and still they are having problems, I was feeling an urge to take a revenge. I always heard that nature takes the great revenge. I always try to forgive people. So that Almighty Lord will forgive me for my sins. But inside I am feeling an urge to take revenge. Am I a bad girl?