User blog comment:FairyRaven/Fairy Tail Chapter 387: Tartarus Arc, Part 4: Father and Son, Review and Commentary/@comment-82.45.146.195-20140609110123/@comment-24800928-20140610004857

they are at least in love (please know that I am joking). I remember watching one of the episodes in the Tenrou arc, and Natsu said he wouldn't help Gray because he knows him well enough to know he wouldn't want the help fighting Ultear (I miss her by the way). Then Happy (like the smartass he is) said (in a perverted way mind you) "you guys have gotten to know each other for a long time." (don't trust that as verbatim). Then, Natsu replies, "don't try to turn this into something dirty" (don't trust that as verbatim). plus they fight all the time to get out that extra tension they have between each other ;).