TV continuity can be tricky. It's impossible to lay the groundwork for a show and have the show go on for multiple decades with feeling the need to tweak a few things. This is the grace we afford to writers and storytellers. And the latest instance of this retcon logic occurred in NCIS: Origins.
The season one finale of the hit prequel series introduced Diane Sterling (Kathleen Kenny), who long time fans will know as the eventual ex-wife of Leroy Jethro Gibbs (Austin Stowell). This is the first time we get to see Sterling, canonically, and as such, the timeline of Gibbs' love life has been tweaked as a way of accommodating the story Origins showrunners want to tell.
Origins will make changes to a Gibbs love triangle

Co-showrunners David J. North and Gina Monreal delved into the tweaks that were made during a recent interview with TV Line. They confirmed that Gibbs and Diane will eventually get married, but noted that Diane's relationship with another NCIS character, Tobias Fornell, has been changed in the franchise timeline.
Diane has a daughter with Tobias Fornell, an FBI Special Agent who appeared on the flagship NCIS series, which has led to some confusion as to whether Diane links up with Gibbs or Fornell first. The answer is unclear because NCIS presented two different versions of what happened. "There are many questions surrounding when Gibbs and Fornell met each other," Monreal noted. "Because it's handled two different ways on the NCIS mothership. One is that they didn’t know each other in the pilot."
What do you do when the source material offers two different paths? Well, you chose the one that best suits the story in the present. Monreal noted that character backstories are prone to change, and the love triangle between Gibbs, Diane, and Tobias is one such instance. "Yes, so those are the sort of times where, when canon disagrees with itself, we have to pick a lane and go with it because we have no other choice," she concluded.
Diane Sterling will play a large role in season 2

Ultimately, however, NCIS: Origins season two will focus on the bond that Gibbs and Diane develop following the tragic car accident that sidelined (and potentially killed) Gibbs' other female confidante, Lala (Mariel Molino). TV Line inquired about the possibility of a time jump between season one and upcoming season two premiere, but Monreal made it clear that nothing has been set in stone.
"There’s a lot of conversations that need to happen about Season two," she admitted. "It's kind of scary but exciting that it can really go a lot of different directions, including who’s there, who we’re watching…" As much as want to see what happened to Lala, we're even more intrigued by the ways in which Diane will impact Gibbs' personal life moving forward.