In my interpretations, this song is about how the relationship is just not how it used to be. Hardships in the relationship kick in and their love for eachother is deteriorating. He still loves her and hopes to work out their differences, but her heart/love has obliterated (faded). "moving mountains" is just a way to say that it's impossible. You can't move mountains, you can only climb over 'em. But obstacles come thru and prevent you from getting to the other side. In the end, he's left all on his own.