"...and tiny little ears, a bit like a hippo's, Daddy says, only purple and hairy. And if you want to call them, you have to hum; they prefer a waltz, nothing too fast-"
-Luna to Dean at Shell Cottage
When Luna was taken off the Hogwarts Express because of what the Quibbler was saying, she was taken to Malfoy Manor, where she met Harry, Hermione, Ron, and Dean. When they were taken back to Shell Cottage, where they were heard briefly talking about the Crumple-Horned Snorkack, which suggests that Dean asked about them, or Luna felt comfortable enough with Dean that she started talking about them.
"Come on, Luna," Dean called as he passed, holding out his free hand; she took it, and followed him back up the stairs.
Later at the Battle of Hogwarts, Dean is going to leave the Room of Requirement, and askes if Luna would like to accompany him. He seems very comfortable with Luna, and she returns the favor, taking his hand and following him up the stairs. It is very possible that the two stayed friends after the war.