Nobody knew of the relationship that Nick and Tony had. Close to the relationship of Clint and Coulson but not quite. It was a relationship born out of the days when Howard Stark used to bring his young son to the base. They would put Tony into "childproof" areas, but more often than not he would find a way out, and Nick Fury would be the one to find him. When Tony was a teenager, he regularly went to Nick for help dealing with his anxiety and other problems. Nick even ended up adding a secret room to his office that was always open for Tony. But when Howard and Maria Stark died, Tony took over the company and grew apart from one of his only father figures. But Nick never stopped caring. He was all too happy to open up that back door and let Tony vent once he became Ironman.