A comic of this headcanon from Young Justice Heacanons Tumblr at [link]
151. The moment that Bruce discovered that he loved Dick like a son was about 7 months after he had moved in. Bruce was in an important business meeting with Lex Luthor, and it was taking all of his self-control not to punch the man square in the face. It was then that he heard a distant shout from down the hall, and looked up to see Dick, on a rolling office chair, being propelled at an amazing speed down the hallway outsid eof the door by the fire extinguisher he was holding, screaming at the top of his lungs, “BRUUUUUUUUUUCE” as he went. Luthor was appalled, but Bruce hadn’t laughed so hard in years.