I agree with Kikipai. I also think this song is about a guy who has been dumped by his girlfriend. Days pass by and he still has feelings for her, but at the same time, as days pass, his heart becomes more cold. He can't remember how it's like to live without her (Where is the life you once had?), and even if she returns to him, he'd have to turn her down (When she will turn to you again
'So long my friend,' is what you'll say).
I agree with Kikipai. I also think this song is about a guy who has been dumped by his girlfriend. Days pass by and he still has feelings for her, but at the same time, as days pass, his heart becomes more cold. He can't remember how it's like to live without her (Where is the life you once had?), and even if she returns to him, he'd have to turn her down (When she will turn to you again 'So long my friend,' is what you'll say).