For those of you who haven't read
Desperation - the basic premise is T'Pol seduces Archer when her pon farr comes along. And it's called Desperation for a reason, the whole situation is meant to be sad. She knows that ethically what she's doing is wrong. In the beginning, she thinks about Trip but decides not to go there. I left the reasons open, but in my mind it was because she didn't want to hurt or use Trip. The implication was that there was still very strong emotion between them.
After I wrote that, I wrote
Dusk which imagines TnT having a long and complicated relationship behind the scenes. I still am amazed at how many TnT-ers were furious with me for that story. I didn't want to write a "everything is awesome, she still loves Trip" behind the scenes story for the episode. I wanted it to be hard for them and to explain why they weren't together in the episode.
Logically, it made a lot of sense to me that at a point, TnT would end up together. They both love Archer. They are the two most senior officers left. They already have an attraction and a deep friendship. So, the friction seen in the episode, in my mind, wouldn't derail the relationship completely. So, I had to come up with a couple of hardships that would explain what we saw.
I got a lot of heat for having them keep their relationship quiet. To me, it was the most natural thing in the world that they would be discreet. Not only because of their positions, but because people might not take well to an inter-species relationship between the colony's two more important people. A lot of people objected to this as well as the fact that they break up for a time.
And yes, Bluetiger, you are right. A caregiver needs a break now and then. I definitely worked that into Dusk as well.