Disclaimer: Not mine.
A/N: This is my take on first times, but takes a detour from canon during the events of Unfinished Business (namely where they slept together then she ran off; in my world, they actually ended up together after that).
First Time
The first time they met, they shook hands and tried to keep from letting Zak see the impact it'd had on both of them. That punch in the gut that was physical attraction, that spark at skin to skin contact that was a hint of something a lot deeper, that indefinable sense of rightness, all needed hiding. She was dating his brother, she believed she loved him, and that was all there was to it.
The first time they flew together, their instructor actually used the term "frakking in the sky with vipers." They were so completely in tune with each other, it was like their hearts were attached and so were their birds, like there was no way one could move without the other. It was the ultimate display of perfect flight, and everyone was surprised she wasn't marrying this brother.
The first time they kissed, they were both drunk. It was during the few days between Zak's funeral and her decision to serve on the Galactica, when they were still speaking. They'd held their own wake, and gotten completely smashed. Even intoxicated, he had enough sense to keep her from doing something he knew she'd regret later, and that could break his heart. He didn't know that she was a lot less drunk than he thought, and that he was breaking her heart.
The first time one of them returned from the dead, they both knew that there was no way to keep from being drawn towards each other. However, in true hard-nosed, take-no-crap, show-no-feelings pilot fashion, they ignored it, and pretended that every time they were in the same room, they ended up mere inches from each other (or touching) by chance.
The first time they gave in, they were both involved with other people, but it didn't matter. They loved each other, they made a concious choice, and it happened. It didn't matter that two people would be heartbroken tomorrow, that bets would be settled and lost. All that mattered was that for this moment, they were together.
The first time they were living together officially, people kept giving him alcohol and her winks. They seemed to think he'd need it, and she didn't need anything.
The first time they put each other in lifestation at the same time, he was having his broken hand and arm splinted - let nobody say Starbuck ever went easy on Apollo, or that she was normal even in labor.