When we get married, what can we do so that our credit is not combined?

Do not open any charge accounts or lines of credit or own anything together.  If you keep your financial lives separate that keeps your "credit" lives separate as well.  But that will preclude you from buying a house together if you intend on being on the mortgage together, having any joint credit cards, etc.  It will really preclude you fro becoming "husband and wife" fully.  You will, though, still be able to file your taxes jointly which saves you more money than "married filing separately."  Give this some thought and see a financial planner.  It is "for better or for worse."