Whenever i'm on facebook he... mixed signals?

whenever i log in to facebook chat, he always says sup? or hey u or something to talk to me. he asks me how my day was and then after that we talk and it'll either get awkward or it'll be steady for about five mins and then die short. then he logs off, and then later logs back on again and tries talking to me again but it always feels awkward. the times we've hung out, it's not awkward at all and he's a great conversationalist. on facebook not so much... does he like me? also, sometimes on facebook he won't even really answer or reply back and logs off. and then logs on, and tries to start talking again. what does this mean? does he like me? we've gone out on a date before...