Star Trek: Voyager's third season episode, Blood Fever, took a big jump in bringing Tom Paris [Robert Duncan McNeill] and B'Elanna Torres [Roxann Dawson] together as a couple. While the duo certainly flirted with one another in the first couple of seasons, it was Blood Fever that really set the stage for the upcoming romance. When Torres is going through the Pon Farr and is trapped in the caves with Paris, things get a little spicy, but originally, it was Tuvok [Tim Russ] who was supposed to be trapped in the caves with B'Elanna.
Tuvok, being Vulcan, would have been able to help B'Elanna through the process, but, at the last minute, literally the day before filming was set to begin, according to Robert Duncan McNeill in Star Trek Monthly, producers decided to go with Tom and B'Elanna being trapped to see where things would go. [Via ScreenRant]
This was a major step forward for the couple and led to them finally expressing their feelings in season four. And while Russ' role was dialed back in the episode, he did still play a major part in helping B'Elanna get through the Vulcan time of mating. It might have actually been strange to have Tuvok and Torres together when she was going through the Pon Farr, especially considering he was married. In the episode, B'Elanna wasn't interested in explanations. And having Tuvok mind-meld with her in an attempt to calm her down would have been an easy way out, if that is what could have happened.
Voyager gave fans Paris and Torres, and the pair were actually a solid couple. With all the turmoil Voyager and its crew was going through, it made sense to have some sense of normalcy aboard, and romance was it. And they were the only couple to make it successfully throughout the entirety of the series which offered a sense of stability as well.