DS9: Meridian

In the third season episode, "Meridian" Jadzia Dax falls in love with... well, actually it doesn't matter. The whole point is that she falls in love with some schmuck and is willing to give her whole way of life up for him. Basically, until Dax and Worf get together, she is DS9's Riker. She's bold, boisterous, up for anything and about once a season she gets all googly-eyed and mushy over some romance that's doomed to fail from the outset.

In "Meridian" she loses her biz over this guy:

"It's not the heat, it's the humanity."

His planet is in a constant state of flux. Every sixty years it disappears and becomes completely incorporeal. Each time the planet returns, it's there for an even shorter span. Dax and this chucklehead work on a way to fix it and eventually come up with a solution. But it won't be sorted before the planet goes into flux again. That means that to stay together these lovebirds will have to make a choice. One will have to leave behind their culture, their people, their whole life, to be with the other and there's no going back for sixty years. Of course Dax decides to stay with him but we all know it can't work out.

I think the problem with these one-episode romances is that we all know what's going to happen. We knew it on TOS and we knew it on Next Gen. Like Kirk and Riker, Dax is sincere in her outpouring of affection but the show is so episodic that no matter how deeply our regular crew member loves their day player, they usually seem like chumps. A few times it works. But then (City on the Edge of Forever, The Outcast) the story is more about the character than the romance. I care about Edith Keeler's crusade. I care about Soren's plight. I love Dax. Unfortunately, I just can't get into Dax's Brigadoon-esque boyfriend of the day.

The high point of this episode for me has always been Jeffrey Combs' first appearance in a Trek series. This dude went on to creep out members of Starfleet in various characters for several years but it all started here, with Combs' playing a pompous ginger sporting a super pervy crush on Kira:

Kira-"Money isn't everything."
Tiron- "No, but it can BUY everything."

The Quark, Kira, Tiron stuff in this one is awesome so even if you can't get into Dax's love story, "Meridian" is still totally worth watching.