Girlfriend
Disclaimer: Sadly, I do not own any of the characters nor do I own Avril Lavigne or the song "Girlfriend". If I did own NCIS and the characters Tony and Ziva would be together and so would Abby and McGee. I apologize if I made any mistakes. Happy reading!
It was extremely late, or early depending on how you looked at it. Yet, Ziva David had decided to remain at her desk. She had told Gibbs that she has some work to finish up, and he had not questioned her despite the fact that she had finished all of her paperwork before hand and the rest of the team had. 'Thank goodness he had not', she thought. That would have been difficult to explain. She needed some time by herself but didn't want to go home for reason even she wasn't really sure of.
Her partner, Tony, had been acting strangely recently. He constantly left work to go to a doctor or dentist appointment and was constantly receiving phone calls from University Hospital. For these reasons she had become concerned that the plague, which she had been informed that he had before she joined Special Agent Gibbs' team, had returned. Later the team found out that he had been working an undercover op for the director and the reason he'd been leaving was to visit his girlfriend. He'd been visiting his girlfriend who just so happened to be the daughter of the arms dealer that he and the director were working to bring down. Jeanne Benoit was her name and she had been a part of Tony and Director Shepherd's mission to capture the arms dealer "La Grenouille" but Tony had ended up falling in love with her and when it ended badly because he'd had to tell her, Jeanne, that he'd been undercover and lied to her about who he was and what he did for a living the entire time they dated, she left him. She told him she wasn't coming back and just abandoned him and all her stuff and left. Later she'd sent Tony a note telling him he had to choose. Meaning, he had to choose between her and NCIS. He'd chosen NCIS but he'd been moody and miserable ever since she left.
When Ziva found out all of that she felt hurt, betrayed and angry. He was her partner. She trusted him and he had lied to her and broken that trust. She had wasted energy worry about him and doing research on the plague, and she'd done all of it for what? Nothing.