Stories that you may have heard and think are credible.
I prefer to talk about stories that I actually know rather than about those that I've heard.
So here is a nice one.
I was in Radom/Poland for my friends' wedding. While I was getting my fancy-polish-wedding-like hairdo done my ex-boyfriend went for a beer and met this very nice, old couple. She was Polish and he was British and they have been married for I don't know how long. From what I can remeber, the biggest issue they had was that people from Poland would breeze in and he wasn't really OK with it.
Also, I know a few Polish girls that have been going out with Belgian and even Moroccan guys for quite a long time now and it works out fine, so I guess it is possible for a non-polish guy to have a normal, long-term relationship with a Polish girl.