Is it possible to be a libertarian and a nationalist at the same time?

A Libertarian can be a Nationalist yes. You can be proud of your country, say you are superior to others but not violate the non-aggression principle.

Does nationalism inherently suggest a feeling of 'supremacy' over others, or could just be a very strong love of your own country and it's values/traditions? I know nationalism doesn't have the nicest ring to it given its history in Europe in the 20s and 30s. Also, where is the line between nationalism and patriotism? How are they different?

Well personally I think that Patriotism is a personal pride, whilst nationalism involved a national identity and and the notion that you or your nation are supreme over others?

Being a nationalist isn't inherently wrong, of course it's natural to believe your country is great. I think the word has been vilified because of people like the Nazis (NATIONAL socialists)

I would say that libertarianism and civic nationalism can go hand-in-hand. Libertarianisn and ethnic nationalism, however, are mutually exclusive concepts.

Libertarians can use ethnic nationalism. Voluntary ethnic separation in accordance with private property rights can be used to create separate ethnic enclaves. Hoppe noted that there can be a racial component to zoning.

Ethnic nationalism involves some form of ethnic cleansing by definition, which inherently violates the NAP.

No it doesn't? Have you ever read the definition?

How does ethnic cleansing not violate the NAP???