Fear of divorce if telling husband that the child is not his

Assalamualaikum, I am a married woman, 2 years ago my husband and I were not in accord and discussed divorce as he no longer found me sexually appealing after having our child, and started having inappropriate conversations with other women, which I uncovered. In my vulnerable state I thought we are heading for divorce and then met a married man who charmed me. I myself am to blame, and had intercourse with him. After that day, that very week my husband wanted intercourse, which I had with him. 2 months later I found out I was pregnant.. After giving birth I contacted the man and asked him if he would do a paternity test. He did, and the child is his not my husbands. My husband and I have been through many ups and downs, but we finally on the road to staying together, Alhamdullilah, Praise be to Allah, However, now I dont know what to do. Im scared of telling my husband as I know he will divorce me. I trully am sorry, and dont want my marriage to end. What can I do? Since the birth of my son, who is 1 years old now I have asked for forgiveness everyday for my weakness.
The married man has 3 daughters with his wife, and I dont want their marriage to end over this either.