Some people say that they are talking about a girl, some say its just Natsu missing his friends or Igneel. I agree with the people who say he is talking about a girl (not because I am a nalu fan) HERE IS SOME PROOF
that is a small hint but . . .
And finally, for those of you out there who still think he's talking about his friends or Igneel. It is obvious they're talking right? Well, would Hiro Mashima hide the fact that he was talking about how much he misses his friends? no he would not. So he probably is talking about a girl. Cause I don't think that nalu is going to cannon with just one chapter so Hiro Mashima probably didn't put words for a reason.