Not allowed to do that
He shouldn't be allowed to do that. Seems to me he is breaking the law. Highway robbery. Contact the local authorities and see what they say.
Take your girl to court
If I were you, I would take your girl to court and fight for custody over the child even though that child is not yours. Sounds like you have been more of a parent to the child then her own mother. I am a mother as well. My daughter is 3. My fiancee is more of a father...
If you go ahead and file for divorce
If you go ahead and file for divorce. At the divorce hearing, the judge will order him to pay support and even add the amount of what is owe in back pay in the child support as well.
It is endangerment of a child
It is considered endangerment of a child if your exhusband knows all about the crimes committed to your daughters. I suggest speaking to the state attorney's office in your state.
Pending on the state and its laws
Pending on the state that you live in and the laws they have against child support and how it is given to one person or taken from one person is different then any other state. I know here in Florida that you have a child who is 18 and enrolled in college...