If the statements were made within the past year they are perhaps defamatory and could be the subject of a slander action (or if written, libel). However, the cost of such an action could far exceed any recovery.
On the other hand it is possible your ex committed some form of harrassment, which would be a criminal complaint. The problem with that is that in the context of a domestic relations case the police and prosecutors tend not to want to get involved.
Call a NY attorney first and foremost. Each state code on defamation is unique. In Virginia, you would not have a claim unless you have been ruined professionally because of this (can't get a new job etc..)
Sadly, I think the best recourse would be to do nothing. I know that is not great legal advice, but it sounds so personal that nothing good could come of filing suit. Do your kids want to watch you sue their Mom? Probably not.
I am sorry - good luck!
Sign up to receive a 3-part series of useful information and advice about personal injury law.