He doesn't say "I love you" anymore?

My bf and I have been dating for about 8 months. He used to tell me that he loved me all the time. But now, every time we hang up or stop chatting online, he never says it. I even say "I love you" and he says nothing. He sometimes answers ":D" or some other joyous interjection, but never actually says it. What does this mean???