I know various Agas, not anyone who would call themselves Agnus, there was an Aggy in the UK which is so ugly - Agnieszka is a pretty name (just as well considering how many of them are around).
I tell my students that unless they desperately want to be called an English name for personal reasons I'm going to call them by their actual name that most people would use (Kasia is a million times nicer than Kate, which is just as well considering how many of them are around!).
To the OP: please don't judge a nation by one person. There's lots of lovely Polish people, I am sure there are also plenty of ******** who are Polish as well as ones who are Irish: the attitude of your recent girlfriend is the way of the world these days not reason to dump someone (was the husband a decent guy? how can one know a whole story). Just saying this to point out that high expectations are the fastest way to disappointment...