Well, I am divorced. So take this with a grain of salt. I would talk to him, or maybe write a letter. I would tell him that I made a terrible mistake, but want my marriage and family. I would explain that you don't blame him finding another woman, but your family deserves better from the two of you. Tell him that if he can't forgive, to go for it, that he is free to do what he wants, but you hope that he will choose his family.