Why is my partner not reporting his ex to the police?

He cheated for years.I live with him(not married)we both have his kids. She found out 1st &she dumped him.I stayed with him on condition he nevers speaks to her again.She has been haring him by phone, email,insulting. He changed his numbers, blocked her emails but she keeps making new email addresses &he won't shut down his email.She's haring me too because i stopped him seeing their child but i dont want to get involved.Why can't he just report her to the POLICE &pls don't tell me because of the child because he doesn't want to be involved with the child anymore so the child won't be dumbed on him if she gets arrested. Am i being unreasonable for being angry as to why he wont report or get restraining order to protect his family, it's pure harment police wld be on her straight away