One is a superset of the other. Fascism is a political ideology which includes Nationalism as one of its central tenets. You can't be a Fascist and not also be a Nationalist. However, one can be a Nationalist and not be a Fascist. read more
I suspect that it a matter of degree. A Nationalist is a person who is extremely proud and protective of his country and will be aptly biased when dealing with international matters affecting his country’s interests. read more
Nationalism doesn't necessarily imply a hatred for foreign countries, or doesn't imply that your country is inherently superior to the rest. Fascism does. Nationalism doesn't mean you support a harsh security policy, where the police has extended powers, and can do quick justice. Fascism does. read more