Can someone explain Nynaeve and Lan to me?

I’m on Book 4 now, just past the point where Nynaeve and the others leave Tear and Lan almost joins them. The relationship between these two is lightly mentioned in each of the previous books, but it still makes no sense to me. I was pretty shocked when it was first mentioned in book 1 because the pair made no sense to me, and nothing since then has made the relationship make any more sense. I suppose they spent a great deal of time together on the initial journey, but the whole series is about similar journeys and no one else is randomly falling in love (outside of the 3 boys of course, but they are ta'veren and the story is almost entirely about how the world magically shapes itself around them).

To be fair, during their farewell scene I really liked how their personalities were contrasted and how their love for each other caused them to act so unlike their usual selves. I hope this foreshadowing for more character development between them down the road. Still, it doesn’t clarify how or why the relationship began. It feels like the author just wanted both of these characters to have romantic interests and paired them up out of convenience, or that he wanted them to end up together later on and couldn’t come up with a way to make them come together organically.

Did I miss something between them early on or am I the only one that feels this way?