Because he can. YOu are allowing it. He will continue to have a hard time breaking from the OW. It is an addiction. He is addicted to what he gets from her. He MAY eventually realize HE needs to stop, or she MAY get tired of the crumbs he is giving her and realize she has to stop talking to him to move on.....but, it will take a long time. The other bad part of him talking to her is it just prolongs the withdrawal. Every time he talks to her he starts all over with the withdrawal process. He needs to stop all contact before you and him will have a chance. YOu need to have a "no contact" policy in place. He says he wants to be with you, then he needs to do the work to make that happen.