After reading this thread yesterday, I went home and went through our facebook messages and selected messages that were relevant to our application. Messages where we were talking about going somewhere, doing something, visiting someone, when we'll next see each other, counting down the days to when we'll next see each other (we did LDR for 4 years) and included pictures to back up the messages.
I.e when we were travelling to San Francisco or New York, we included an iconic photo of the places, i.e us with the golden gate bridge or Empire State building in the back ground etc.
I found it the easiest screen shotting the messages including the date and the nice thing with facebook messages are they include the time too.
I then pasted them into a word document in chronological order - oldest ---> latest. - I printed 10 pages with the screenshots, 2-3 on some pages of the message log.
Hope this helps!