User blog comment:IamJakuhoRaikoben/Chapter 412: Dance Unto Ishgar, Review./@comment-24729244-20141209083045/@comment-9595671-20141209131509

And I remember in one blog someone mentioned the couples that Mashima seems to be trying to make obvious are NatsuxLucy, GrayxJuvia, JellalxErza, GajeelxLevy, HappyxCarla and ElfmanxEvergreen. And I've seen enough examples for all of them that I believe that user.

There might be more I haven't noticed though, and there can be occasional instances with others, but I think we know some of the more obvious couples atleast.