See, I think I've just conflated Gibbs with a very stonefaced version of Jack Harkness -- up for anything, but only with the right person. So he is epically into Abby and they play a lot of dirty games together and she's okay that he sometimes brings Tony around because wow, Tony and Gibbs, right? And poor Tony would just keep pining otherwise. Even though Abby and Gibbs both know that Tony and McGee are pretty much destined to be together.

And Ducky is totally the ex that he eventually became best friends with. :D Which is why whenever anyone's having issues with Gibbs, HAVE YOU NOTICED, they go to Ducky. :D