This is his way of keeping some control over you -- it's a power trip. Take that power away by limiting your contact with him; through emails is one way, as long as he isn't abusive in them as well. You could get a close friend to filter them for you, if you need to (I did that with an abusive relative once; I sent his emails to another relative and I never actually read them).
I realize that you have to keep in contact becuz of your child, but limit it to just that and nothing more. I have a friend who is going through something similar -- and she just told him up front that name calling would not be tolerated; if he continues, the contact will be severely limited and/or stopped altogether until he talks in a respectful manner to both of them.

and prayers for you and your child ...