This answer contains spoilers…
(view spoiler)[It's like a metaphor for their love and a reflection of how hard it was for them to love and spend time with each other. Every time they did meet though, they danced, so I think that's the reference. (hide spoiler)]
There is a couple of references to dancing in the book, both quite important in the story line but I took the phrase to mean - Enjoy what you have while you can as you don't know what is around the corner.