I'd agree that sometimes people make too much of the distinction -- people you like and agree with are patriots, those you hate are nationalists -- but there really was a difference between the kind of feeling we have for our country and people in the US, Britain or Canada, and the feeling that Germany's nationalists had in the years leading up to WWI.
The more you reflect on the distinction the fuzzier it may seem but we do need two words.
G.K. Chesterton summed it up by saying that a patriot loves his country as he loves his mother, because she is his mother. A nationalist has to believe that his country is better than all other countries or his mother is better than all the other mothers in the world.
The patriot recognizes flaws in one's own country and still loves his motherland, while the nationalist refuses to admit any flaws or weaknesses in his country (except perhaps those attributable to internal enemies and subversives or weaklings).
Things get complicated, though, when you combine the nationalism-patriotism distinction with the distinction between ethnic and civic nationalism.
The use of the term liberal has evolved since the time of the founders.
In the 1700’s a (Classic) “Liberal” was an anti-Statist (Anti-Monarchist).
Today the use of the term “Liberal” indicates a Marxist Statist.
Tell this to a Lib and watch their head explode.
They can play legal weasel word games with this. But that is how it is.