He always says.....?:\?

A guy I'm friends with just says "bye" or "ttyl" or "nite" in the middle of convos. If he needs to go, he could atleast say "ok I'm going to sleep now. I'll ttyl bye luv u". I mean we aren't going out but he could be a little nicer!!!! Because whenever I have 2 go I say something lk "byeee ily ttyl nite:)''. All he says is like one word and randomly 2.....I don't like it. Why does he do that? Could it mean he isn't interested???