How old are your girls?  And you talk to your children after he says this right and assure them in the most gentle way a mother could that you are not going to die, you are healthy, and sometimes people say things that are not true and this thing that he has said, is not true.
You should probably guard them, guard thier hearts and don't let him play with thier emotions.
I'm experiancing something similar and something was said to my 7 year old last week and it was a way for him to get at me through her and it turns my stomach that he'd do such a thing. I don't even know if he realizes it.  It's not right.  And my children have boundries and I will protect them.  This is my first experiance of going through matters such as this. I call my Pastor when I have to for support, I love my church family.  Remember to lean on the people around you when you need to...that's what they are there for.  And guard your heart and guard your children's hearts. Be the better person and maintain your dignity.  The children do not need to be in the middle of this dispute.
hugs to you,
gretchen