Where on earth has it been reported that the woman was his ex wife? There was no divorce. No custody battle. He didn't know about the child until recently -- reportedly hadn't met him until he was on life support
-- and even the mother could only narrow it to one of two guys before the paternity test.
Peterson has been dating the same woman since he was at Oklahoma. They have a son together that is also two years old. So unless there was some mishap at a sperm donation clinic he slept with multiple women at the same time. While not a crime, this can have consequences. He behaved irresponsibly, and it led to the worst possible result.