What are valid reasons to end the marriage to your children's father?

It's worst for the kids to live through this. Maybe leaving will wake him up. He may not have hurt them physically but mentally it's hurting them. The kids are watching him and this is all that they will know and possibly grow up to be the same way. Kids grow up to be just like their parents because they don't know any other way. Tell your friend to get out while she can and save herself and the kids from all this abuse.