I think it is worth drawing a distinction between nationalism and patriotism.
I am extremely patriotic. I am proud to come from a country from which have come some of the greatest thinkers, scientists, writers and artists the world has ever known. I am proud that when I go to watch City I travel across a street named after the English man that invented the computer. I am proud that the man who invented the hyper text transfer protocol (basically, the technique that allows the internet to exist in its modern form) is a compatriot of mine. I am proud that we as a nation stood up to fascism and bankrupted ourselves to do it, because it was the right thing to do. I am proud that the English breakfast (or Scottish, for those north of the border) and the Sunday roast is at least the equal of any meal from any culture in the world. I am proud of our architecture, and the beauty of our landscape. I am proud that we were the first nation to abolish slavery and to police that on the high seas because it was the right thing to do. I am proud that the world speaks our language, and plays our games, and that large areas of the planet follow our laws, and have adopted our system of government and democracy, because people from Hull and Stockport and Brighton and Yeovil went and built new societies across the world. And until 2016 I was proud that we were a tolerant nation and were not beset by many of the national insecurities that affected places like the US, Australia and (dare I say it) Ireland. I'm also proud that we are the first and only nation to win the world cups in football rugby and cricket. I have no difficulty with other nations being equally proud of their cultures and heritage - if I came from the land of Yeats and Joyce I'd be proud of them too - but that's what I fee about mine, and I will happily argue the toss with anyone who says otherwise.
I am not in the least nationalistic. I regard nationalism as being exclusionary, and fundamentally xenophobic. It is not I think in itself racist, but it seems to me that it is a short step from nationalism to racism. It is about being better than you rather than being the best we can be. It is about scapegoating others and not taking responsibility for your own problems. It is a poisonous and twisted view that gratifies its adherents not by taking simple pride in the achievements of its own tribe, but by doing so in order to demonstrate its apparent superiority to others.
It's the difference, if you like, between the Wolves fans last Sunday who were genuinely delighted that their team had gone away and beaten the champions of England in their back yard, because that's some achievement, and those who felt better about themselves because having watched their team they then hurled abuse and gestures and made threats of violence towards the fans of the team they had just beaten from behind the safety of a 10 foot high metal fence.