My wife is having extramarital affair. I want my custody of son

My wife is having an extra marital affair. I had caught her before as well but then she promised that it was a her mistake and won't repeat for sake of the family. I had forgiven her and given her a chance. But I recently found out that she is still having relationship with him. We both belong from Muslim background. Let me also mention that my wife lives in her mother's house from last 1.5 month .for this Case please give me a suggestion. I would like to take my child responsibility. Our family can't leave without my child plz help