I have 2 daughters and my problem is that a few months before my wife told me that she was raped. after few days she agree and they have intercourse. I divorce her or I forgive her??

I have 2 daughters and my problem is that a few months before my wife told me that I had raped through my cousin. My wife was already in 2nd or 3rd month of pregnancy at that time. She afraid to tell me because of divorce. My cousin come to my home regularly in my presence or absence, when I m not at home my wife allow him to enter the home. When this thing happened I didn?t doubt to my wife because I trust on her, but after few weeks I note that some thing is wrong with both of them then I doubt her but I didn?t ask her. But after few months my wife take me in confidence and told me she raped. I request her to tell the truth either she raped or both of you agreed upon this. She swears upon Allah and said that she was raped. I also ask that man that why he do so, in first he didn?t accept any thing and he said that both of us didn?t do any thing but when I force him he told me that at first I (means my cousin) ask to her to do so but she didn?t agree but after few days she agree and they have intercourse with each other. Please help me I divorce her or I forgive her or any other Islamic rule please tell me.