Hi Cherry,
It's nice to read such letters like yours. I'm a Polish man and I used to date an American girl when I was about 25. But unlike you, we were sort of similar - we both were "serious and stern" and we agreed on most things. We were even going to get married, but the distance between us eventually killed the relationship (she was finishing her college in NY and I was starting mine in Chicago).
I think Polish men are in general more "mature" than their American peers; while American men often tend to act like children until their old days, Polish guys take life and relationship more seriously. I, for example, dated only two girls by the age of 25 (an American guy at the same age would have "tried out" dozens of different girls).
I don't know his background, but his being brush may be because he wants to show he is "tough" (when in fact he may be romantic). Also, he may still think a little strange and "worse" than his American peers (eg. he may not have as nice car as they have, he may not have family/friends here).
I ended up marrying a Polish girl and I'm happy, but sometimes I think about my American date too

.