Nina had been dating with Will, who moved in with her.
In Divide Us, Nina conducted a post-mortem examination on a patient of Natalie's who had died due to a condition they missed. Nina fast-tracked it and went personally to give her the results, with the intentions of possibly making Natalie feel guilty, which she did. When Will found out that she personally did this, he went down to ask her, after telling Natalie that it was something anyone could've and would've missed. Nina admitted she was jealous of him and Natalie because they're always together. He reassured her they were just friends and promised to spend more time with her.
In Love Hurts, Will realised he had feelings for Natalie after a talk with Jay. He broke up with Nina, who was heartbroken and replied that she knew he had feelings for Natalie and that he'd been lying to her.