Since CSI's first season there were hints that both Sara Sidle and Grissom were interested in each other romantically. In fact creators made Sara Sidle while thinking of a future love interest for Grissom, but during the show's first three seasons Grissom flirted with all the female characters, and when Sara asked him out to dinner he rejected her, claiming that he does not know what to do about what is going on between them.
In season four Grissom's true feelings are revealed in "Butterflied", an episode that centers entirely around him discovering his sentiments for Sara. It was then that he admitted not being able to risk his career to be with her. In this season Sara apparently develops a drinking problem, which Grissom acknowledges on the season finale; after this they would hardly see each other, and Grissom becomes interested in detective Sofia Curtis.
In mid-season five, Sara is suspended for insubordination and she reveals to Grissom her tormented childhood. He refuses to fire her and has her working in every case of the next two seasons with him.
It was not until the sixth season finale that it is revealed that Grissom and Sara have worked through whatever issues they had, and are, in fact, a couple, and have been for two years. This revelation caused mix reviews among critics, some of them see this relationship as CSI "jumping the shark", an attempt to include more drama and romance to the show, so as to be able to compete with the medical drama Grey's Anatomy, which airs in the US at the same time. By killing off the sexual tension between the two characters and making them an item, the production crew were seen to be adding more personal drama to the show, increasing the appeal to some of Grey's Anatomy's younger audience. This has been denied by the writers, Carol Mendelsohn even said that she has never been able to see Grissom with someone else other than Sara and that this episode was seen as the writers as the right time to reveal the relationship, Jorja Fox and William Petersen have also admitted that the relationship is not new.
Throughout season seven the audience sees Grissom and Sara as a couple, but the relationship is kept secret from the others in the lab until Sara's abduction by The Miniature Killer in the season finale. During the 2007-2008 season, season eight, they have become engaged to be married. In CSIs eighth season, when Jorja Fox decided to leave the show, both she and the writers decided not to kill the character, so as to leave the doors open for a possible comeback. Consequently, Sara Sidle is submerged into depression after her kidnap in the season seven finale, and, even though she accepts Grissom's marriage proposal on the season's fourth episode, she shows signs of burnout during the subsequent episodes, breaking down on the season's seventh episode, leaving Las Vegas and the CSI's with only a goodbye letter for Grissom and a good luck note for Ronnie Lake. In the letter she claims that ever since her father's death she has been dealing with "ghosts" and that she now needs to go away and deal with them before self-destructing.