make sure you be polite with everyone!
generally, yes. civil : adhering to the norms of polite social intercourse; not deficient in common courtesy polite: showing good manners toward others, as in behavior, speech, etc.; courteous; civil
nice, ethical
Act polite means to be kind and if you don't know what kind means it means to be nice.
Well, it could be that he likes you. Another option though is that he has a past with this other girl and is not very fond of her. It really depends.
"civil", "civilised", "civilized", "cultivated", "cultured" and "genteel"