If  my husband and myself purchased a house 2 months before we married and he put $80,000 down, after 18 years of marriage is he entitled to get that money back?

This is going to be tricky.  He is saying that it was separate property and that he used it and now he wants it back off the top ion the divorce, correct?  He can try and make that srgument.  What you are going to argue is that it was his intent to make the monet marital funds by using it to purchase the marital home. How it will come out depends on your state case law.  Seek legal help.  Good luck.