We obviously know right from the beginning his use of past tense exemplifies that the relationship he was in was great, but ended. I believe however that the main message of the song is not just to mention that his relationship died. I think the artist wants his audience to realize that relationships may seem great in the beginning, but you never know how its going to work out until you've spent time with them.

When the song reads, "In the beginning we had nothing to hide" the artist is conveying that you must be trustworthy in a relationship as well which ends up making him not care about her anymore. Basically, "if you can't be trustworthy why would I remain with you" is what he's trying to say.

BROAD MEANING- I feel as if the artist is saying you must overcome obstacles in a relationship to make it last, or both partners lose interest and everything goes to shit. We each have different ways of interpreting this piece but this is my most general interpretation.