Nationalism is loving the idea of loving your nation rather than actually loving it
That could be summed up in picture form with Trump hugging the flag.
Nationalism is a person thinking everyone is of one mind, one appearance, homogeneous, etc. rather than wanting to face the truth that a nation is made up of many different people from different colors, cultures, religions, etc.
Nationalism is saying your country is great... but yet it's so fragile at the same time in the nationalist's eyes. "We're full" so no more immigrants, we have the "greatest healthcare system in the world" but a five year old refugee producing mucus can cause it all to come crashing down.
Nationalism is loving the past, even if that past is imaginary, rather than loving the present and hoping for a better future. I dare anyone to describe a happy and healthy relationship that idealizes the past, hates the present, and fears the future.
I think I've got it: The nationalist 'loves' their country not unlike how Annie Wilkes loved Paul Sheldon.