There are some people in the world that just love having an “It’s Complicated” status on Facebook.
You two were never official, and I’m willing to bet it was more his idea than yours. And now he’s playing this “I miss you but I can’t miss you” game. My guess here is that he’s going to be moving on, but wants to keep you on the hook just enough that you’ll be around in case he changes his mind.
It’s a dirty game to play, but one that gets played a lot. So my advice is to move on from this non-relationship and work towards getting an actual one. The difference between what this one and what you’ll have with a good guy will be huge.